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 $192.47   11.661%   $214.9139   $214.91   $214.90   $214.90  
  Purchase #2 $140.38   4.426%   $146.5932   $146.59   $146.60   $146.60  
  Purchase #3 $20.26   11.762%   $22.643   $22.64   $22.65   $22.60  
  Purchase #4 $241.66   7.647%   $260.1397   $260.14   $260.15   $260.10  
  Purchase #5 $232.40   11.826%   $259.8836   $259.88   $259.90   $259.90  
  Purchase #6 $211.78   5.332%   $223.0721   $223.07   $223.05   $223.10  
  Purchase #7 $113.39   11.729%   $126.6895   $126.69   $126.70   $126.70  
  7 purchase totals = $1,152.34       $1,253.9350   $1,253.92   $1,253.95   $1,253.90