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 $54.77   10.591%   $60.5707   $60.57   $60.55   $60.60  
  Purchase #2 $152.62   3.442%   $157.8732   $157.87   $157.85   $157.90  
  Purchase #3 $11.31   12.420%   $12.7147   $12.71   $12.70   $12.70  
  Purchase #4 $199.90   4.673%   $209.2413   $209.24   $209.25   $209.20  
  Purchase #5 $95.55   4.566%   $99.9128   $99.91   $99.90   $99.90  
  Purchase #6 $209.97   9.376%   $229.6568   $229.66   $229.65   $229.70  
  Purchase #7 $189.47   6.797%   $202.3483   $202.35   $202.35   $202.30  
  7 purchase totals = $913.59       $972.3178   $972.31   $972.25   $972.30