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 $94.39   11.569%   $105.31   $105.31   $105.30   $105.30  
  Purchase #2 $23.43   3.725%   $24.3028   $24.30   $24.30   $24.30  
  Purchase #3 $45.77   10.183%   $50.4308   $50.43   $50.45   $50.40  
  Purchase #4 $165.71   13.801%   $188.5796   $188.58   $188.60   $188.60  
  Purchase #5 $193.30   12.571%   $217.5997   $217.60   $217.60   $217.60  
  Purchase #6 $95.38   6.239%   $101.3308   $101.33   $101.35   $101.30  
  Purchase #7 $245.94   12.770%   $277.3465   $277.35   $277.35   $277.30  
  7 purchase totals = $863.92       $964.9002   $964.90   $964.95   $964.80