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 $220.34   11.765%   $246.263   $246.26   $246.25   $246.30  
  Purchase #2 $144.58   3.209%   $149.2196   $149.22   $149.20   $149.20  
  Purchase #3 $30.87   12.528%   $34.7374   $34.74   $34.75   $34.70  
  Purchase #4 $155.41   10.315%   $171.4405   $171.44   $171.45   $171.40  
  Purchase #5 $72.56   5.295%   $76.4021   $76.40   $76.40   $76.40  
  Purchase #6 $170.27   7.667%   $183.3246   $183.32   $183.30   $183.30  
  Purchase #7 $142.31   9.223%   $155.4353   $155.44   $155.45   $155.40  
  7 purchase totals = $936.34       $1,016.8225   $1,016.82   $1,016.80   $1,016.70