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 $94.76   7.359%   $101.7334   $101.73   $101.75   $101.70  
  Purchase #2 $148.95   7.811%   $160.5845   $160.58   $160.60   $160.60  
  Purchase #3 $60.26   13.388%   $68.3276   $68.33   $68.35   $68.30  
  Purchase #4 $73.99   10.264%   $81.5843   $81.58   $81.60   $81.60  
  Purchase #5 $237.64   11.191%   $264.2343   $264.23   $264.25   $264.20  
  Purchase #6 $87.41   4.413%   $91.2674   $91.27   $91.25   $91.30  
  Purchase #7 $88.69   11.122%   $98.5541   $98.55   $98.55   $98.60  
  7 purchase totals = $791.70       $866.2856   $866.27   $866.35   $866.30