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 $140.52   11.855%   $157.1786   $157.18   $157.20   $157.20  
  Purchase #2 $67.49   11.266%   $75.0934   $75.09   $75.10   $75.10  
  Purchase #3 $85.59   5.771%   $90.5294   $90.53   $90.55   $90.50  
  Purchase #4 $84.36   12.583%   $94.975   $94.98   $95.00   $95.00  
  Purchase #5 $59.88   9.797%   $65.7464   $65.75   $65.75   $65.70  
  Purchase #6 $33.51   5.130%   $35.2291   $35.23   $35.25   $35.20  
  Purchase #7 $239.56   5.836%   $253.5407   $253.54   $253.55   $253.50  
  7 purchase totals = $710.91       $772.2926   $772.30   $772.40   $772.20