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 $48.85   8.587%   $53.0447   $53.04   $53.05   $53.00  
  Purchase #2 $201.92   10.861%   $223.8505   $223.85   $223.85   $223.90  
  Purchase #3 $223.75   6.472%   $238.2311   $238.23   $238.25   $238.20  
  Purchase #4 $201.63   13.207%   $228.2593   $228.26   $228.25   $228.30  
  Purchase #5 $146.57   8.454%   $158.961   $158.96   $158.95   $159.00  
  Purchase #6 $24.37   12.130%   $27.3261   $27.33   $27.35   $27.30  
  Purchase #7 $100.98   4.219%   $105.2403   $105.24   $105.25   $105.20  
  7 purchase totals = $948.07       $1,034.9130   $1,034.91   $1,034.95   $1,034.90