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 $68.65   11.185%   $76.3285   $76.33   $76.35   $76.30  
  Purchase #2 $101.57   11.519%   $113.2698   $113.27   $113.25   $113.30  
  Purchase #3 $152.45   12.114%   $170.9178   $170.92   $170.90   $170.90  
  Purchase #4 $172.61   6.397%   $183.6519   $183.65   $183.65   $183.70  
  Purchase #5 $56.62   12.598%   $63.753   $63.75   $63.75   $63.80  
  Purchase #6 $33.93   12.682%   $38.233   $38.23   $38.25   $38.20  
  Purchase #7 $166.93   7.634%   $179.6734   $179.67   $179.65   $179.70  
  7 purchase totals = $752.76       $825.8274   $825.82   $825.80   $825.90