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 $55.29   13.493%   $62.7503   $62.75   $62.75   $62.80  
  Purchase #2 $24.79   10.695%   $27.4413   $27.44   $27.45   $27.40  
  Purchase #3 $213.26   7.618%   $229.5061   $229.51   $229.50   $229.50  
  Purchase #4 $70.86   4.336%   $73.9325   $73.93   $73.95   $73.90  
  Purchase #5 $24.56   8.152%   $26.5621   $26.56   $26.55   $26.60  
  Purchase #6 $100.74   10.682%   $111.501   $111.50   $111.50   $111.50  
  Purchase #7 $34.89   5.577%   $36.8358   $36.84   $36.85   $36.80  
  7 purchase totals = $524.39       $568.5291   $568.53   $568.55   $568.50