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 $68.53   13.206%   $77.5801   $77.58   $77.60   $77.60  
  Purchase #2 $56.62   10.261%   $62.4298   $62.43   $62.45   $62.40  
  Purchase #3 $189.35   4.604%   $198.0677   $198.07   $198.05   $198.10  
  Purchase #4 $152.96   3.149%   $157.7767   $157.78   $157.80   $157.80  
  Purchase #5 $55.93   4.524%   $58.4603   $58.46   $58.45   $58.50  
  Purchase #6 $146.64   13.734%   $166.7795   $166.78   $166.80   $166.80  
  Purchase #7 $21.25   3.166%   $21.9228   $21.92   $21.90   $21.90  
  7 purchase totals = $691.28       $743.0169   $743.02   $743.05   $743.10