Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $178.45   10.406%   $197.0195   $197.02   $197.00   $197.00  
  Purchase #2 $199.26   13.555%   $226.2697   $226.27   $226.25   $226.30  
  Purchase #3 $158.53   12.814%   $178.844   $178.84   $178.85   $178.80  
  Purchase #4 $175.67   11.758%   $196.3253   $196.33   $196.35   $196.30  
  Purchase #5 $239.60   13.178%   $271.1745   $271.17   $271.15   $271.20  
  Purchase #6 $152.77   11.673%   $170.6028   $170.60   $170.60   $170.60  
  Purchase #7 $177.83   5.376%   $187.3901   $187.39   $187.40   $187.40  
  7 purchase totals = $1,282.11       $1,427.6259   $1,427.62   $1,427.60   $1,427.60