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 $195.27   12.531%   $219.7393   $219.74   $219.75   $219.70  
  Purchase #2 $135.72   11.525%   $151.3617   $151.36   $151.35   $151.40  
  Purchase #3 $162.54   4.500%   $169.8543   $169.85   $169.85   $169.90  
  Purchase #4 $239.87   5.428%   $252.8901   $252.89   $252.90   $252.90  
  Purchase #5 $46.59   10.149%   $51.3184   $51.32   $51.30   $51.30  
  Purchase #6 $136.97   9.806%   $150.4013   $150.40   $150.40   $150.40  
  Purchase #7 $245.95   7.615%   $264.6791   $264.68   $264.70   $264.70  
  7 purchase totals = $1,162.91       $1,260.2442   $1,260.24   $1,260.25   $1,260.30