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 $207.86   7.266%   $222.9631   $222.96   $222.95   $223.00  
  Purchase #2 $114.52   8.780%   $124.5749   $124.57   $124.55   $124.60  
  Purchase #3 $53.76   8.809%   $58.4957   $58.50   $58.50   $58.50  
  Purchase #4 $7.46   5.663%   $7.8825   $7.88   $7.90   $7.90  
  Purchase #5 $104.41   11.677%   $116.602   $116.60   $116.60   $116.60  
  Purchase #6 $225.47   10.420%   $248.964   $248.96   $248.95   $249.00  
  Purchase #7 $15.34   5.733%   $16.2194   $16.22   $16.20   $16.20  
  7 purchase totals = $728.82       $795.7016   $795.69   $795.65   $795.80