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 $53.45   8.570%   $58.0307   $58.03   $58.05   $58.00  
  Purchase #2 $129.56   11.118%   $143.9645   $143.96   $143.95   $144.00  
  Purchase #3 $75.85   8.589%   $82.3648   $82.36   $82.35   $82.40  
  Purchase #4 $233.59   11.511%   $260.4785   $260.48   $260.50   $260.50  
  Purchase #5 $242.54   4.747%   $254.0534   $254.05   $254.05   $254.10  
  Purchase #6 $162.65   11.189%   $180.8489   $180.85   $180.85   $180.80  
  Purchase #7 $197.98   7.127%   $212.09   $212.09   $212.10   $212.10  
  7 purchase totals = $1,095.62       $1,191.8308   $1,191.82   $1,191.85   $1,191.90