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 $188.87   8.602%   $205.1166   $205.12   $205.10   $205.10  
  Purchase #2 $54.61   13.559%   $62.0146   $62.01   $62.00   $62.00  
  Purchase #3 $44.32   13.237%   $50.1866   $50.19   $50.20   $50.20  
  Purchase #4 $87.95   10.726%   $97.3835   $97.38   $97.40   $97.40  
  Purchase #5 $96.55   5.374%   $101.7386   $101.74   $101.75   $101.70  
  Purchase #6 $200.75   11.506%   $223.8483   $223.85   $223.85   $223.80  
  Purchase #7 $36.49   8.533%   $39.6037   $39.60   $39.60   $39.60  
  7 purchase totals = $709.54       $779.8919   $779.89   $779.90   $779.80