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 $58.94   6.182%   $62.5837   $62.58   $62.60   $62.60  
  Purchase #2 $185.67   7.254%   $199.1385   $199.14   $199.15   $199.10  
  Purchase #3 $232.98   9.392%   $254.8615   $254.86   $254.85   $254.90  
  Purchase #4 $126.54   5.674%   $133.7199   $133.72   $133.70   $133.70  
  Purchase #5 $121.67   10.806%   $134.8177   $134.82   $134.80   $134.80  
  Purchase #6 $174.99   11.149%   $194.4996   $194.50   $194.50   $194.50  
  Purchase #7 $86.38   6.356%   $91.8703   $91.87   $91.85   $91.90  
  7 purchase totals = $987.17       $1,071.4912   $1,071.49   $1,071.45   $1,071.50