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 $192.66   7.559%   $207.2232   $207.22   $207.20   $207.20  
  Purchase #2 $48.97   13.554%   $55.6074   $55.61   $55.60   $55.60  
  Purchase #3 $146.37   6.726%   $156.2148   $156.21   $156.20   $156.20  
  Purchase #4 $178.78   13.705%   $203.2818   $203.28   $203.30   $203.30  
  Purchase #5 $35.84   10.554%   $39.6226   $39.62   $39.60   $39.60  
  Purchase #6 $155.67   6.513%   $165.8088   $165.81   $165.80   $165.80  
  Purchase #7 $92.78   3.610%   $96.1294   $96.13   $96.15   $96.10  
  7 purchase totals = $851.07       $923.8880   $923.88   $923.85   $923.80