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 $23.29   11.761%   $26.0291   $26.03   $26.05   $26.00  
  Purchase #2 $24.97   5.540%   $26.3533   $26.35   $26.35   $26.40  
  Purchase #3 $126.26   10.790%   $139.8835   $139.88   $139.90   $139.90  
  Purchase #4 $102.95   4.661%   $107.7485   $107.75   $107.75   $107.70  
  Purchase #5 $62.25   7.267%   $66.7737   $66.77   $66.75   $66.80  
  Purchase #6 $192.94   6.205%   $204.9119   $204.91   $204.90   $204.90  
  Purchase #7 $178.30   11.114%   $198.1163   $198.12   $198.10   $198.10  
  7 purchase totals = $710.96       $769.8163   $769.81   $769.80   $769.80