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 $154.57   10.848%   $171.3378   $171.34   $171.35   $171.30  
  Purchase #2 $13.53   8.150%   $14.6327   $14.63   $14.65   $14.60  
  Purchase #3 $74.56   10.389%   $82.306   $82.31   $82.30   $82.30  
  Purchase #4 $96.99   10.104%   $106.7899   $106.79   $106.80   $106.80  
  Purchase #5 $169.99   13.872%   $193.571   $193.57   $193.55   $193.60  
  Purchase #6 $62.68   6.295%   $66.6257   $66.63   $66.65   $66.60  
  Purchase #7 $222.77   13.606%   $253.0801   $253.08   $253.10   $253.10  
  7 purchase totals = $795.09       $888.3432   $888.35   $888.40   $888.30