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 $237.50   6.858%   $253.7878   $253.79   $253.80   $253.80  
  Purchase #2 $212.94   10.427%   $235.1433   $235.14   $235.15   $235.10  
  Purchase #3 $65.70   5.866%   $69.554   $69.55   $69.55   $69.60  
  Purchase #4 $11.42   9.482%   $12.5028   $12.50   $12.50   $12.50  
  Purchase #5 $95.60   4.537%   $99.9374   $99.94   $99.95   $99.90  
  Purchase #6 $207.55   8.607%   $225.4138   $225.41   $225.40   $225.40  
  Purchase #7 $59.72   10.787%   $66.162   $66.16   $66.15   $66.20  
  7 purchase totals = $890.43       $962.5011   $962.49   $962.50   $962.50