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 $208.81   12.689%   $235.3059   $235.31   $235.30   $235.30  
  Purchase #2 $30.36   6.428%   $32.3115   $32.31   $32.30   $32.30  
  Purchase #3 $153.42   10.631%   $169.7301   $169.73   $169.75   $169.70  
  Purchase #4 $202.75   8.537%   $220.0588   $220.06   $220.05   $220.10  
  Purchase #5 $192.61   9.155%   $210.2434   $210.24   $210.25   $210.20  
  Purchase #6 $139.66   12.131%   $156.6022   $156.60   $156.60   $156.60  
  Purchase #7 $217.25   5.772%   $229.7897   $229.79   $229.80   $229.80  
  7 purchase totals = $1,144.86       $1,254.0416   $1,254.04   $1,254.05   $1,254.00