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 $239.40   5.316%   $252.1265   $252.13   $252.15   $252.10  
  Purchase #2 $202.84   4.840%   $212.6575   $212.66   $212.65   $212.70  
  Purchase #3 $231.76   6.855%   $247.6471   $247.65   $247.65   $247.60  
  Purchase #4 $216.48   13.132%   $244.9082   $244.91   $244.90   $244.90  
  Purchase #5 $58.86   7.497%   $63.2727   $63.27   $63.25   $63.30  
  Purchase #6 $249.96   12.166%   $280.3701   $280.37   $280.35   $280.40  
  Purchase #7 $152.89   10.349%   $168.7126   $168.71   $168.70   $168.70  
  7 purchase totals = $1,352.19       $1,469.6947   $1,469.70   $1,469.65   $1,469.70