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 $208.26   3.707%   $215.9802   $215.98   $216.00   $216.00  
  Purchase #2 $240.79   3.392%   $248.9576   $248.96   $248.95   $249.00  
  Purchase #3 $81.39   5.430%   $85.8095   $85.81   $85.80   $85.80  
  Purchase #4 $56.59   4.776%   $59.2927   $59.29   $59.30   $59.30  
  Purchase #5 $44.27   10.377%   $48.8639   $48.86   $48.85   $48.90  
  Purchase #6 $108.68   4.436%   $113.501   $113.50   $113.50   $113.50  
  Purchase #7 $236.83   12.726%   $266.969   $266.97   $266.95   $267.00  
  7 purchase totals = $976.81       $1,039.3739   $1,039.37   $1,039.35   $1,039.50