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 $190.25   12.327%   $213.7021   $213.70   $213.70   $213.70  
  Purchase #2 $58.88   9.726%   $64.6067   $64.61   $64.60   $64.60  
  Purchase #3 $242.51   5.177%   $255.0647   $255.06   $255.05   $255.10  
  Purchase #4 $110.35   11.111%   $122.611   $122.61   $122.60   $122.60  
  Purchase #5 $164.88   7.558%   $177.3416   $177.34   $177.35   $177.30  
  Purchase #6 $173.39   11.537%   $193.394   $193.39   $193.40   $193.40  
  Purchase #7 $23.96   7.637%   $25.7898   $25.79   $25.80   $25.80  
  7 purchase totals = $964.22       $1,052.5099   $1,052.50   $1,052.50   $1,052.50