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 $166.94   9.806%   $183.3101   $183.31   $183.30   $183.30  
  Purchase #2 $193.87   4.153%   $201.9214   $201.92   $201.90   $201.90  
  Purchase #3 $217.26   10.602%   $240.2939   $240.29   $240.30   $240.30  
  Purchase #4 $171.85   8.334%   $186.172   $186.17   $186.15   $186.20  
  Purchase #5 $66.43   8.829%   $72.2951   $72.30   $72.30   $72.30  
  Purchase #6 $68.78   8.252%   $74.4557   $74.46   $74.45   $74.50  
  Purchase #7 $218.88   9.368%   $239.3847   $239.38   $239.40   $239.40  
  7 purchase totals = $1,104.01       $1,197.8329   $1,197.83   $1,197.80   $1,197.90