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 $193.47   12.161%   $216.9979   $217.00   $217.00   $217.00  
  Purchase #2 $229.63   11.179%   $255.3003   $255.30   $255.30   $255.30  
  Purchase #3 $223.96   7.620%   $241.0258   $241.03   $241.05   $241.00  
  Purchase #4 $70.29   8.117%   $75.9954   $76.00   $76.00   $76.00  
  Purchase #5 $11.96   4.766%   $12.53   $12.53   $12.55   $12.50  
  Purchase #6 $241.93   4.759%   $253.4434   $253.44   $253.45   $253.40  
  Purchase #7 $201.82   12.209%   $226.4602   $226.46   $226.45   $226.50  
  7 purchase totals = $1,173.06       $1,281.7530   $1,281.76   $1,281.80   $1,281.70