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 $217.95   4.121%   $226.9317   $226.93   $226.95   $226.90  
  Purchase #2 $88.35   8.835%   $96.1557   $96.16   $96.15   $96.20  
  Purchase #3 $125.60   6.412%   $133.6535   $133.65   $133.65   $133.70  
  Purchase #4 $154.54   13.271%   $175.049   $175.05   $175.05   $175.00  
  Purchase #5 $9.67   3.593%   $10.0174   $10.02   $10.00   $10.00  
  Purchase #6 $239.82   5.223%   $252.3458   $252.35   $252.35   $252.30  
  Purchase #7 $157.93   8.275%   $170.9987   $171.00   $171.00   $171.00  
  7 purchase totals = $993.86       $1,065.1518   $1,065.16   $1,065.15   $1,065.10