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 $180.38   12.761%   $203.3983   $203.40   $203.40   $203.40  
  Purchase #2 $136.25   11.340%   $151.7008   $151.70   $151.70   $151.70  
  Purchase #3 $139.88   12.322%   $157.116   $157.12   $157.10   $157.10  
  Purchase #4 $61.68   11.295%   $68.6468   $68.65   $68.65   $68.60  
  Purchase #5 $214.62   10.147%   $236.3975   $236.40   $236.40   $236.40  
  Purchase #6 $185.69   4.831%   $194.6607   $194.66   $194.65   $194.70  
  Purchase #7 $73.32   10.393%   $80.9401   $80.94   $80.95   $80.90  
  7 purchase totals = $991.82       $1,092.8602   $1,092.87   $1,092.85   $1,092.80