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 $167.60   11.714%   $187.2327   $187.23   $187.25   $187.20  
  Purchase #2 $22.56   13.441%   $25.5923   $25.59   $25.60   $25.60  
  Purchase #3 $96.92   13.637%   $110.137   $110.14   $110.15   $110.10  
  Purchase #4 $249.57   8.713%   $271.315   $271.32   $271.30   $271.30  
  Purchase #5 $106.70   8.487%   $115.7556   $115.76   $115.75   $115.80  
  Purchase #6 $99.99   12.415%   $112.4038   $112.40   $112.40   $112.40  
  Purchase #7 $179.45   9.131%   $195.8356   $195.84   $195.85   $195.80  
  7 purchase totals = $922.79       $1,018.2720   $1,018.28   $1,018.30   $1,018.20