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 $106.96   11.269%   $119.0133   $119.01   $119.00   $119.00  
  Purchase #2 $139.67   8.688%   $151.8045   $151.80   $151.80   $151.80  
  Purchase #3 $167.57   3.816%   $173.9645   $173.96   $173.95   $174.00  
  Purchase #4 $203.54   12.105%   $228.1785   $228.18   $228.20   $228.20  
  Purchase #5 $104.69   12.866%   $118.1594   $118.16   $118.15   $118.20  
  Purchase #6 $10.68   13.731%   $12.1465   $12.15   $12.15   $12.10  
  Purchase #7 $60.30   12.632%   $67.9171   $67.92   $67.90   $67.90  
  7 purchase totals = $793.41       $871.1838   $871.18   $871.15   $871.20