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 $207.73   12.509%   $233.7149   $233.71   $233.70   $233.70  
  Purchase #2 $117.68   3.578%   $121.8906   $121.89   $121.90   $121.90  
  Purchase #3 $13.37   8.625%   $14.5232   $14.52   $14.50   $14.50  
  Purchase #4 $86.94   9.391%   $95.1045   $95.10   $95.10   $95.10  
  Purchase #5 $214.35   3.870%   $222.6453   $222.65   $222.65   $222.60  
  Purchase #6 $238.42   8.793%   $259.3843   $259.38   $259.40   $259.40  
  Purchase #7 $233.67   11.464%   $260.4579   $260.46   $260.45   $260.50  
  7 purchase totals = $1,112.16       $1,207.7207   $1,207.71   $1,207.70   $1,207.70