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 $241.28   6.229%   $256.3093   $256.31   $256.30   $256.30  
  Purchase #2 $217.88   11.374%   $242.6617   $242.66   $242.65   $242.70  
  Purchase #3 $93.93   3.520%   $97.2363   $97.24   $97.25   $97.20  
  Purchase #4 $56.68   13.723%   $64.4582   $64.46   $64.45   $64.50  
  Purchase #5 $192.71   9.198%   $210.4355   $210.44   $210.45   $210.40  
  Purchase #6 $232.47   4.497%   $242.9242   $242.92   $242.90   $242.90  
  Purchase #7 $183.53   7.191%   $196.7276   $196.73   $196.75   $196.70  
  7 purchase totals = $1,218.48       $1,310.7528   $1,310.76   $1,310.75   $1,310.70