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 $57.97   13.248%   $65.6499   $65.65   $65.65   $65.60  
  Purchase #2 $131.86   13.335%   $149.4435   $149.44   $149.45   $149.40  
  Purchase #3 $46.96   6.391%   $49.9612   $49.96   $49.95   $50.00  
  Purchase #4 $123.57   12.169%   $138.6072   $138.61   $138.60   $138.60  
  Purchase #5 $109.87   5.459%   $115.8678   $115.87   $115.85   $115.90  
  Purchase #6 $203.82   10.506%   $225.2333   $225.23   $225.25   $225.20  
  Purchase #7 $20.98   11.288%   $23.3482   $23.35   $23.35   $23.30  
  7 purchase totals = $695.03       $768.1111   $768.11   $768.10   $768.00