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 $62.85   10.223%   $69.2752   $69.28   $69.30   $69.30  
  Purchase #2 $83.28   13.106%   $94.1947   $94.19   $94.20   $94.20  
  Purchase #3 $197.29   4.761%   $206.683   $206.68   $206.70   $206.70  
  Purchase #4 $154.86   7.782%   $166.9112   $166.91   $166.90   $166.90  
  Purchase #5 $133.95   12.172%   $150.2544   $150.25   $150.25   $150.30  
  Purchase #6 $90.51   12.612%   $101.9251   $101.93   $101.95   $101.90  
  Purchase #7 $197.65   11.509%   $220.3975   $220.40   $220.40   $220.40  
  7 purchase totals = $920.39       $1,009.6411   $1,009.64   $1,009.70   $1,009.70