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 $228.81   5.320%   $240.9827   $240.98   $241.00   $241.00  
  Purchase #2 $124.26   10.825%   $137.7111   $137.71   $137.70   $137.70  
  Purchase #3 $146.37   13.713%   $166.4417   $166.44   $166.45   $166.40  
  Purchase #4 $44.77   11.787%   $50.047   $50.05   $50.05   $50.00  
  Purchase #5 $22.59   10.404%   $24.9403   $24.94   $24.95   $24.90  
  Purchase #6 $242.36   8.870%   $263.8573   $263.86   $263.85   $263.90  
  Purchase #7 $69.60   3.849%   $72.2789   $72.28   $72.30   $72.30  
  7 purchase totals = $878.76       $956.2590   $956.26   $956.30   $956.20