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 $213.94   11.185%   $237.8692   $237.87   $237.85   $237.90  
  Purchase #2 $84.38   9.734%   $92.5935   $92.59   $92.60   $92.60  
  Purchase #3 $61.70   7.496%   $66.325   $66.33   $66.35   $66.30  
  Purchase #4 $49.62   13.182%   $56.1609   $56.16   $56.15   $56.20  
  Purchase #5 $201.98   11.335%   $224.8744   $224.87   $224.85   $224.90  
  Purchase #6 $95.69   11.822%   $107.0025   $107.00   $107.00   $107.00  
  Purchase #7 $113.29   7.223%   $121.4729   $121.47   $121.45   $121.50  
  7 purchase totals = $820.60       $906.2984   $906.29   $906.25   $906.40