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 $52.95   6.234%   $56.2509   $56.25   $56.25   $56.30  
  Purchase #2 $171.53   13.616%   $194.8855   $194.89   $194.90   $194.90  
  Purchase #3 $26.66   13.516%   $30.2634   $30.26   $30.25   $30.30  
  Purchase #4 $39.44   9.364%   $43.1332   $43.13   $43.15   $43.10  
  Purchase #5 $185.49   12.852%   $209.3292   $209.33   $209.35   $209.30  
  Purchase #6 $171.62   9.785%   $188.413   $188.41   $188.40   $188.40  
  Purchase #7 $216.29   7.824%   $233.2125   $233.21   $233.20   $233.20  
  7 purchase totals = $863.98       $955.4877   $955.48   $955.50   $955.50