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 $58.63   8.427%   $63.5708   $63.57   $63.55   $63.60  
  Purchase #2 $49.69   9.259%   $54.2908   $54.29   $54.30   $54.30  
  Purchase #3 $178.68   12.572%   $201.1436   $201.14   $201.15   $201.10  
  Purchase #4 $71.81   11.824%   $80.3008   $80.30   $80.30   $80.30  
  Purchase #5 $214.91   7.559%   $231.155   $231.16   $231.15   $231.20  
  Purchase #6 $34.30   8.429%   $37.1911   $37.19   $37.20   $37.20  
  Purchase #7 $61.85   7.796%   $66.6718   $66.67   $66.65   $66.70  
  7 purchase totals = $669.87       $734.3239   $734.32   $734.30   $734.40