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 $86.83   10.766%   $96.1781   $96.18   $96.20   $96.20  
  Purchase #2 $147.79   13.120%   $167.18   $167.18   $167.20   $167.20  
  Purchase #3 $117.34   13.353%   $133.0084   $133.01   $133.00   $133.00  
  Purchase #4 $101.28   4.108%   $105.4406   $105.44   $105.45   $105.40  
  Purchase #5 $8.88   13.870%   $10.1117   $10.11   $10.10   $10.10  
  Purchase #6 $173.41   6.571%   $184.8048   $184.80   $184.80   $184.80  
  Purchase #7 $188.44   5.696%   $199.1735   $199.17   $199.15   $199.20  
  7 purchase totals = $823.97       $895.8971   $895.89   $895.90   $895.90