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 $236.46   13.253%   $267.798   $267.80   $267.80   $267.80  
  Purchase #2 $193.54   9.367%   $211.6689   $211.67   $211.65   $211.70  
  Purchase #3 $62.28   4.169%   $64.8765   $64.88   $64.90   $64.90  
  Purchase #4 $16.55   6.540%   $17.6324   $17.63   $17.65   $17.60  
  Purchase #5 $249.99   13.798%   $284.4836   $284.48   $284.50   $284.50  
  Purchase #6 $166.88   8.255%   $180.6559   $180.66   $180.65   $180.70  
  Purchase #7 $14.31   3.805%   $14.8545   $14.85   $14.85   $14.90  
  7 purchase totals = $940.01       $1,041.9698   $1,041.97   $1,042.00   $1,042.10