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 $131.95   7.815%   $142.2619   $142.26   $142.25   $142.30  
  Purchase #2 $48.44   5.308%   $51.0112   $51.01   $51.00   $51.00  
  Purchase #3 $49.96   8.215%   $54.0642   $54.06   $54.05   $54.10  
  Purchase #4 $202.79   7.168%   $217.326   $217.33   $217.35   $217.30  
  Purchase #5 $192.26   6.721%   $205.1818   $205.18   $205.20   $205.20  
  Purchase #6 $146.82   7.197%   $157.3866   $157.39   $157.40   $157.40  
  Purchase #7 $37.42   8.271%   $40.515   $40.52   $40.50   $40.50  
  7 purchase totals = $809.64       $867.7467   $867.75   $867.75   $867.80