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 $45.98   8.615%   $49.9412   $49.94   $49.95   $49.90  
  Purchase #2 $238.93   5.448%   $251.9469   $251.95   $251.95   $251.90  
  Purchase #3 $87.51   8.634%   $95.0656   $95.07   $95.05   $95.10  
  Purchase #4 $144.47   6.167%   $153.3795   $153.38   $153.40   $153.40  
  Purchase #5 $239.32   7.473%   $257.2044   $257.20   $257.20   $257.20  
  Purchase #6 $222.52   7.543%   $239.3047   $239.30   $239.30   $239.30  
  Purchase #7 $190.39   13.432%   $215.9632   $215.96   $215.95   $216.00  
  7 purchase totals = $1,169.12       $1,262.8055   $1,262.80   $1,262.80   $1,262.80