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 $245.28   6.593%   $261.4513   $261.45   $261.45   $261.50  
  Purchase #2 $202.41   3.635%   $209.7676   $209.77   $209.75   $209.80  
  Purchase #3 $95.51   7.607%   $102.7754   $102.78   $102.80   $102.80  
  Purchase #4 $51.41   7.626%   $55.3305   $55.33   $55.35   $55.30  
  Purchase #5 $35.25   4.757%   $36.9268   $36.93   $36.95   $36.90  
  Purchase #6 $59.82   5.402%   $63.0515   $63.05   $63.05   $63.10  
  Purchase #7 $181.39   6.265%   $192.7541   $192.75   $192.75   $192.80  
  7 purchase totals = $871.07       $922.0572   $922.06   $922.10   $922.20