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 $217.51   13.835%   $247.6025   $247.60   $247.60   $247.60  
  Purchase #2 $53.68   5.478%   $56.6206   $56.62   $56.60   $56.60  
  Purchase #3 $244.25   5.256%   $257.0878   $257.09   $257.10   $257.10  
  Purchase #4 $70.50   9.458%   $77.1679   $77.17   $77.15   $77.20  
  Purchase #5 $37.28   7.859%   $40.2098   $40.21   $40.20   $40.20  
  Purchase #6 $143.86   6.744%   $153.5619   $153.56   $153.55   $153.60  
  Purchase #7 $177.62   6.382%   $188.9557   $188.96   $188.95   $189.00  
  7 purchase totals = $944.70       $1,021.2062   $1,021.21   $1,021.15   $1,021.30