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 $188.40   4.768%   $197.3829   $197.38   $197.40   $197.40  
  Purchase #2 $215.56   10.103%   $237.338   $237.34   $237.35   $237.30  
  Purchase #3 $108.40   9.129%   $118.2958   $118.30   $118.30   $118.30  
  Purchase #4 $129.77   12.284%   $145.7109   $145.71   $145.70   $145.70  
  Purchase #5 $217.37   3.784%   $225.5953   $225.60   $225.60   $225.60  
  Purchase #6 $215.72   13.282%   $244.3719   $244.37   $244.35   $244.40  
  Purchase #7 $223.62   5.743%   $236.4625   $236.46   $236.45   $236.50  
  7 purchase totals = $1,298.84       $1,405.1573   $1,405.16   $1,405.15   $1,405.20