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 $163.73   8.281%   $177.2885   $177.29   $177.30   $177.30  
  Purchase #2 $150.96   10.213%   $166.3775   $166.38   $166.40   $166.40  
  Purchase #3 $156.49   13.599%   $177.7711   $177.77   $177.75   $177.80  
  Purchase #4 $111.85   6.836%   $119.4961   $119.50   $119.50   $119.50  
  Purchase #5 $117.39   7.284%   $125.9407   $125.94   $125.95   $125.90  
  Purchase #6 $166.50   5.165%   $175.0997   $175.10   $175.10   $175.10  
  Purchase #7 $129.55   8.217%   $140.1951   $140.20   $140.20   $140.20  
  7 purchase totals = $996.47       $1,082.1687   $1,082.18   $1,082.20   $1,082.20