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 $96.77   3.201%   $99.8676   $99.87   $99.85   $99.90  
  Purchase #2 $177.62   11.333%   $197.7497   $197.75   $197.75   $197.70  
  Purchase #3 $98.29   11.693%   $109.783   $109.78   $109.80   $109.80  
  Purchase #4 $76.74   12.475%   $86.3133   $86.31   $86.30   $86.30  
  Purchase #5 $204.34   6.598%   $217.8224   $217.82   $217.80   $217.80  
  Purchase #6 $24.37   4.850%   $25.5519   $25.55   $25.55   $25.60  
  Purchase #7 $78.80   11.694%   $88.0149   $88.01   $88.00   $88.00  
  7 purchase totals = $756.93       $825.1028   $825.09   $825.05   $825.10