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 $68.62   11.660%   $76.6211   $76.62   $76.60   $76.60  
  Purchase #2 $56.94   10.334%   $62.8242   $62.82   $62.80   $62.80  
  Purchase #3 $40.34   11.313%   $44.9037   $44.90   $44.90   $44.90  
  Purchase #4 $225.32   5.540%   $237.8027   $237.80   $237.80   $237.80  
  Purchase #5 $149.62   6.841%   $159.8555   $159.86   $159.85   $159.90  
  Purchase #6 $44.85   12.295%   $50.3643   $50.36   $50.35   $50.40  
  Purchase #7 $48.72   3.133%   $50.2464   $50.25   $50.25   $50.20  
  7 purchase totals = $634.41       $682.6179   $682.61   $682.55   $682.60