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 $118.49   10.518%   $130.9528   $130.95   $130.95   $131.00  
  Purchase #2 $77.80   4.514%   $81.3119   $81.31   $81.30   $81.30  
  Purchase #3 $164.44   5.142%   $172.8955   $172.90   $172.90   $172.90  
  Purchase #4 $12.67   13.631%   $14.397   $14.40   $14.40   $14.40  
  Purchase #5 $240.42   8.585%   $261.0601   $261.06   $261.05   $261.10  
  Purchase #6 $62.27   3.278%   $64.3112   $64.31   $64.30   $64.30  
  Purchase #7 $17.52   13.644%   $19.9104   $19.91   $19.90   $19.90  
  7 purchase totals = $693.61       $744.8389   $744.84   $744.80   $744.90