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 $218.52   12.697%   $246.2655   $246.27   $246.25   $246.30  
  Purchase #2 $113.39   10.332%   $125.1055   $125.11   $125.10   $125.10  
  Purchase #3 $119.84   10.244%   $132.1164   $132.12   $132.10   $132.10  
  Purchase #4 $129.77   6.647%   $138.3958   $138.40   $138.40   $138.40  
  Purchase #5 $84.91   6.590%   $90.5056   $90.51   $90.50   $90.50  
  Purchase #6 $249.98   3.604%   $258.9893   $258.99   $259.00   $259.00  
  Purchase #7 $84.95   9.208%   $92.7722   $92.77   $92.75   $92.80  
  7 purchase totals = $1,001.36       $1,084.1503   $1,084.17   $1,084.10   $1,084.20