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 $61.76   5.770%   $65.3236   $65.32   $65.30   $65.30  
  Purchase #2 $104.79   9.285%   $114.5198   $114.52   $114.50   $114.50  
  Purchase #3 $29.67   13.470%   $33.6665   $33.67   $33.65   $33.70  
  Purchase #4 $53.57   6.817%   $57.2219   $57.22   $57.20   $57.20  
  Purchase #5 $224.87   9.314%   $245.8144   $245.81   $245.80   $245.80  
  Purchase #6 $193.57   6.690%   $206.5198   $206.52   $206.50   $206.50  
  Purchase #7 $103.71   5.826%   $109.7521   $109.75   $109.75   $109.80  
  7 purchase totals = $771.94       $832.8181   $832.81   $832.70   $832.80