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 $59.61   11.670%   $66.5665   $66.57   $66.55   $66.60  
  Purchase #2 $94.30   5.631%   $99.61   $99.61   $99.60   $99.60  
  Purchase #3 $94.77   5.653%   $100.1273   $100.13   $100.15   $100.10  
  Purchase #4 $204.45   6.532%   $217.8047   $217.80   $217.80   $217.80  
  Purchase #5 $49.54   13.760%   $56.3567   $56.36   $56.35   $56.40  
  Purchase #6 $88.91   8.525%   $96.4896   $96.49   $96.50   $96.50  
  Purchase #7 $119.81   13.322%   $135.7711   $135.77   $135.75   $135.80  
  7 purchase totals = $711.39       $772.7259   $772.73   $772.70   $772.80