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 $113.75   9.298%   $124.3265   $124.33   $124.35   $124.30  
  Purchase #2 $57.55   8.808%   $62.619   $62.62   $62.60   $62.60  
  Purchase #3 $195.62   5.674%   $206.7195   $206.72   $206.70   $206.70  
  Purchase #4 $65.80   5.358%   $69.3256   $69.33   $69.35   $69.30  
  Purchase #5 $49.59   11.632%   $55.3583   $55.36   $55.35   $55.40  
  Purchase #6 $57.45   7.778%   $61.9185   $61.92   $61.90   $61.90  
  Purchase #7 $22.58   13.578%   $25.6459   $25.65   $25.65   $25.60  
  7 purchase totals = $562.34       $605.9133   $605.93   $605.90   $605.80