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 $210.73   11.426%   $234.808   $234.81   $234.80   $234.80  
  Purchase #2 $116.37   5.666%   $122.9635   $122.96   $122.95   $123.00  
  Purchase #3 $35.29   13.201%   $39.9486   $39.95   $39.95   $39.90  
  Purchase #4 $156.89   3.759%   $162.7875   $162.79   $162.80   $162.80  
  Purchase #5 $136.77   10.452%   $151.0652   $151.07   $151.05   $151.10  
  Purchase #6 $127.30   12.664%   $143.4213   $143.42   $143.40   $143.40  
  Purchase #7 $155.78   7.856%   $168.0181   $168.02   $168.00   $168.00  
  7 purchase totals = $939.13       $1,023.0122   $1,023.02   $1,022.95   $1,023.00