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 $48.73   9.866%   $53.5377   $53.54   $53.55   $53.50  
  Purchase #2 $189.88   12.719%   $214.0308   $214.03   $214.05   $214.00  
  Purchase #3 $90.38   12.534%   $101.7082   $101.71   $101.70   $101.70  
  Purchase #4 $182.79   13.597%   $207.644   $207.64   $207.65   $207.60  
  Purchase #5 $134.51   6.568%   $143.3446   $143.34   $143.35   $143.30  
  Purchase #6 $130.97   10.186%   $144.3106   $144.31   $144.30   $144.30  
  Purchase #7 $67.82   7.220%   $72.7166   $72.72   $72.70   $72.70  
  7 purchase totals = $845.08       $937.2925   $937.29   $937.30   $937.10