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 $91.53   5.271%   $96.3545   $96.35   $96.35   $96.40  
  Purchase #2 $74.92   3.356%   $77.4343   $77.43   $77.45   $77.40  
  Purchase #3 $20.44   10.774%   $22.6422   $22.64   $22.65   $22.60  
  Purchase #4 $171.92   13.820%   $195.6793   $195.68   $195.70   $195.70  
  Purchase #5 $132.56   4.669%   $138.7492   $138.75   $138.75   $138.70  
  Purchase #6 $250.72   5.676%   $264.9509   $264.95   $264.95   $265.00  
  Purchase #7 $141.57   12.352%   $159.0567   $159.06   $159.05   $159.10  
  7 purchase totals = $883.66       $954.8671   $954.86   $954.90   $954.90