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 $53.34   4.700%   $55.847   $55.85   $55.85   $55.80  
  Purchase #2 $56.64   8.243%   $61.3088   $61.31   $61.30   $61.30  
  Purchase #3 $40.35   3.187%   $41.636   $41.64   $41.65   $41.60  
  Purchase #4 $109.69   11.238%   $122.017   $122.02   $122.00   $122.00  
  Purchase #5 $39.76   3.501%   $41.152   $41.15   $41.15   $41.20  
  Purchase #6 $20.89   10.856%   $23.1578   $23.16   $23.15   $23.20  
  Purchase #7 $246.76   5.323%   $259.895   $259.90   $259.90   $259.90  
  7 purchase totals = $567.43       $605.0136   $605.03   $605.00   $605.00