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 $64.87   13.658%   $73.7299   $73.73   $73.75   $73.70  
  Purchase #2 $54.58   4.457%   $57.0126   $57.01   $57.00   $57.00  
  Purchase #3 $212.63   4.273%   $221.7157   $221.72   $221.70   $221.70  
  Purchase #4 $132.64   4.316%   $138.3647   $138.36   $138.35   $138.40  
  Purchase #5 $41.78   12.537%   $47.018   $47.02   $47.00   $47.00  
  Purchase #6 $175.71   13.620%   $199.6417   $199.64   $199.65   $199.60  
  Purchase #7 $117.53   8.249%   $127.225   $127.23   $127.25   $127.20  
  7 purchase totals = $799.74       $864.7076   $864.71   $864.70   $864.60