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 $41.40   4.603%   $43.3056   $43.31   $43.30   $43.30  
  Purchase #2 $154.71   3.179%   $159.6282   $159.63   $159.65   $159.60  
  Purchase #3 $92.73   3.335%   $95.8225   $95.82   $95.80   $95.80  
  Purchase #4 $27.82   12.462%   $31.2869   $31.29   $31.30   $31.30  
  Purchase #5 $54.47   6.779%   $58.1625   $58.16   $58.15   $58.20  
  Purchase #6 $147.51   4.446%   $154.0683   $154.07   $154.05   $154.10  
  Purchase #7 $185.69   11.359%   $206.7825   $206.78   $206.80   $206.80  
  7 purchase totals = $704.33       $749.0565   $749.06   $749.05   $749.10