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 $226.93   11.850%   $253.8212   $253.82   $253.80   $253.80  
  Purchase #2 $231.36   10.298%   $255.1855   $255.19   $255.20   $255.20  
  Purchase #3 $83.29   12.652%   $93.8279   $93.83   $93.85   $93.80  
  Purchase #4 $113.86   4.796%   $119.3207   $119.32   $119.30   $119.30  
  Purchase #5 $50.75   7.628%   $54.6212   $54.62   $54.60   $54.60  
  Purchase #6 $99.73   3.765%   $103.4848   $103.48   $103.50   $103.50  
  Purchase #7 $66.42   5.320%   $69.9535   $69.95   $69.95   $70.00  
  7 purchase totals = $872.34       $950.2148   $950.21   $950.20   $950.20