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 $248.89   6.168%   $264.2415   $264.24   $264.25   $264.20  
  Purchase #2 $56.58   5.446%   $59.6613   $59.66   $59.65   $59.70  
  Purchase #3 $62.54   7.401%   $67.1686   $67.17   $67.15   $67.20  
  Purchase #4 $58.91   9.109%   $64.2761   $64.28   $64.30   $64.30  
  Purchase #5 $95.30   11.648%   $106.4005   $106.40   $106.40   $106.40  
  Purchase #6 $195.56   9.434%   $214.0091   $214.01   $214.00   $214.00  
  Purchase #7 $7.28   8.800%   $7.9206   $7.92   $7.90   $7.90  
  7 purchase totals = $725.06       $783.6777   $783.68   $783.65   $783.70