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 $235.69   7.107%   $252.4405   $252.44   $252.45   $252.40  
  Purchase #2 $173.54   6.722%   $185.2054   $185.21   $185.20   $185.20  
  Purchase #3 $48.61   7.336%   $52.176   $52.18   $52.20   $52.20  
  Purchase #4 $27.50   4.763%   $28.8098   $28.81   $28.80   $28.80  
  Purchase #5 $67.37   12.715%   $75.9361   $75.94   $75.95   $75.90  
  Purchase #6 $195.38   7.145%   $209.3399   $209.34   $209.35   $209.30  
  Purchase #7 $200.40   4.546%   $209.5102   $209.51   $209.50   $209.50  
  7 purchase totals = $948.49       $1,013.4179   $1,013.43   $1,013.45   $1,013.30