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 $245.44   8.769%   $266.9626   $266.96   $266.95   $267.00  
  Purchase #2 $206.29   6.141%   $218.9583   $218.96   $218.95   $219.00  
  Purchase #3 $42.36   12.317%   $47.5775   $47.58   $47.60   $47.60  
  Purchase #4 $111.39   12.733%   $125.5733   $125.57   $125.55   $125.60  
  Purchase #5 $54.86   11.385%   $61.1058   $61.11   $61.10   $61.10  
  Purchase #6 $169.28   7.368%   $181.7526   $181.75   $181.75   $181.80  
  Purchase #7 $108.88   11.484%   $121.3838   $121.38   $121.40   $121.40  
  7 purchase totals = $938.50       $1,023.3139   $1,023.31   $1,023.30   $1,023.50