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 $222.75   9.354%   $243.586   $243.59   $243.60   $243.60  
  Purchase #2 $21.75   8.458%   $23.5896   $23.59   $23.60   $23.60  
  Purchase #3 $86.62   13.787%   $98.5623   $98.56   $98.55   $98.60  
  Purchase #4 $223.63   12.554%   $251.7045   $251.70   $251.70   $251.70  
  Purchase #5 $181.57   5.674%   $191.8723   $191.87   $191.85   $191.90  
  Purchase #6 $23.99   8.832%   $26.1088   $26.11   $26.10   $26.10  
  Purchase #7 $221.65   9.317%   $242.3011   $242.30   $242.30   $242.30  
  7 purchase totals = $981.96       $1,077.7246   $1,077.72   $1,077.70   $1,077.80