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 $233.67   5.714%   $247.0219   $247.02   $247.00   $247.00  
  Purchase #2 $104.28   12.714%   $117.5382   $117.54   $117.55   $117.50  
  Purchase #3 $41.28   13.701%   $46.9358   $46.94   $46.95   $46.90  
  Purchase #4 $183.55   8.744%   $199.5996   $199.60   $199.60   $199.60  
  Purchase #5 $61.78   9.411%   $67.5941   $67.59   $67.60   $67.60  
  Purchase #6 $158.42   11.330%   $176.369   $176.37   $176.35   $176.40  
  Purchase #7 $51.97   4.255%   $54.1813   $54.18   $54.20   $54.20  
  7 purchase totals = $834.95       $909.2399   $909.24   $909.25   $909.20