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 $71.96   8.318%   $77.9456   $77.95   $77.95   $77.90  
  Purchase #2 $91.36   3.675%   $94.7175   $94.72   $94.70   $94.70  
  Purchase #3 $17.80   4.626%   $18.6234   $18.62   $18.60   $18.60  
  Purchase #4 $233.93   13.428%   $265.3421   $265.34   $265.35   $265.30  
  Purchase #5 $54.95   6.241%   $58.3794   $58.38   $58.40   $58.40  
  Purchase #6 $98.55   8.342%   $106.771   $106.77   $106.75   $106.80  
  Purchase #7 $153.91   11.399%   $171.4542   $171.45   $171.45   $171.50  
  7 purchase totals = $722.46       $793.2332   $793.23   $793.20   $793.20