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 $164.94   11.210%   $183.4298   $183.43   $183.45   $183.40  
  Purchase #2 $186.89   8.466%   $202.7121   $202.71   $202.70   $202.70  
  Purchase #3 $113.85   9.747%   $124.947   $124.95   $124.95   $124.90  
  Purchase #4 $44.93   7.560%   $48.3267   $48.33   $48.35   $48.30  
  Purchase #5 $180.76   10.497%   $199.7344   $199.73   $199.75   $199.70  
  Purchase #6 $240.32   13.721%   $273.2943   $273.29   $273.30   $273.30  
  Purchase #7 $27.78   4.874%   $29.134   $29.13   $29.15   $29.10  
  7 purchase totals = $959.47       $1,061.5783   $1,061.57   $1,061.65   $1,061.40