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 $227.71   6.127%   $241.6618   $241.66   $241.65   $241.70  
  Purchase #2 $56.75   3.459%   $58.713   $58.71   $58.70   $58.70  
  Purchase #3 $119.63   8.424%   $129.7076   $129.71   $129.70   $129.70  
  Purchase #4 $205.54   5.229%   $216.2877   $216.29   $216.30   $216.30  
  Purchase #5 $43.57   7.742%   $46.9432   $46.94   $46.95   $46.90  
  Purchase #6 $179.67   10.265%   $198.1131   $198.11   $198.10   $198.10  
  Purchase #7 $51.65   10.178%   $56.9069   $56.91   $56.90   $56.90  
  7 purchase totals = $884.52       $948.3333   $948.33   $948.30   $948.30