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 $60.25   5.282%   $63.4324   $63.43   $63.45   $63.40  
  Purchase #2 $206.38   13.601%   $234.4497   $234.45   $234.45   $234.40  
  Purchase #3 $116.60   12.282%   $130.9208   $130.92   $130.90   $130.90  
  Purchase #4 $149.51   3.571%   $154.849   $154.85   $154.85   $154.80  
  Purchase #5 $5.45   5.735%   $5.7626   $5.76   $5.75   $5.80  
  Purchase #6 $97.37   13.308%   $110.328   $110.33   $110.35   $110.30  
  Purchase #7 $38.71   13.163%   $43.8054   $43.81   $43.80   $43.80  
  7 purchase totals = $674.27       $743.5479   $743.55   $743.55   $743.40