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 $90.61   5.378%   $95.483   $95.48   $95.50   $95.50  
  Purchase #2 $190.28   8.213%   $205.9077   $205.91   $205.90   $205.90  
  Purchase #3 $112.63   4.125%   $117.276   $117.28   $117.30   $117.30  
  Purchase #4 $104.58   4.746%   $109.5434   $109.54   $109.55   $109.50  
  Purchase #5 $104.49   8.645%   $113.5232   $113.52   $113.50   $113.50  
  Purchase #6 $142.51   12.286%   $160.0188   $160.02   $160.00   $160.00  
  Purchase #7 $153.74   5.432%   $162.0912   $162.09   $162.10   $162.10  
  7 purchase totals = $898.84       $963.8433   $963.84   $963.85   $963.80