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 $56.97   12.860%   $64.2963   $64.30   $64.30   $64.30  
  Purchase #2 $214.99   13.145%   $243.2504   $243.25   $243.25   $243.30  
  Purchase #3 $164.82   13.244%   $186.6488   $186.65   $186.65   $186.60  
  Purchase #4 $193.27   6.185%   $205.2237   $205.22   $205.20   $205.20  
  Purchase #5 $6.70   3.184%   $6.9133   $6.91   $6.90   $6.90  
  Purchase #6 $212.96   5.418%   $224.4982   $224.50   $224.50   $224.50  
  Purchase #7 $25.36   8.155%   $27.4281   $27.43   $27.45   $27.40  
  7 purchase totals = $875.07       $958.2588   $958.26   $958.25   $958.20