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 $165.90   4.471%   $173.3174   $173.32   $173.30   $173.30  
  Purchase #2 $194.59   11.850%   $217.6489   $217.65   $217.65   $217.60  
  Purchase #3 $118.64   13.116%   $134.2008   $134.20   $134.20   $134.20  
  Purchase #4 $185.49   10.458%   $204.8885   $204.89   $204.90   $204.90  
  Purchase #5 $86.61   8.297%   $93.796   $93.80   $93.80   $93.80  
  Purchase #6 $179.40   3.804%   $186.2244   $186.22   $186.20   $186.20  
  Purchase #7 $183.38   5.844%   $194.0967   $194.10   $194.10   $194.10  
  7 purchase totals = $1,114.01       $1,204.1727   $1,204.18   $1,204.15   $1,204.10