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 $234.29   9.232%   $255.9197   $255.92   $255.90   $255.90  
  Purchase #2 $14.53   3.236%   $15.0002   $15.00   $15.00   $15.00  
  Purchase #3 $44.67   8.549%   $48.4888   $48.49   $48.50   $48.50  
  Purchase #4 $24.33   13.232%   $27.5493   $27.55   $27.55   $27.50  
  Purchase #5 $153.28   7.714%   $165.104   $165.10   $165.10   $165.10  
  Purchase #6 $153.35   11.669%   $171.2444   $171.24   $171.25   $171.20  
  Purchase #7 $102.79   10.847%   $113.9396   $113.94   $113.95   $113.90  
  7 purchase totals = $727.24       $797.2460   $797.24   $797.25   $797.10