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 $64.39   6.556%   $68.6114   $68.61   $68.60   $68.60  
  Purchase #2 $45.81   8.317%   $49.62   $49.62   $49.60   $49.60  
  Purchase #3 $89.53   11.564%   $99.8832   $99.88   $99.90   $99.90  
  Purchase #4 $248.41   5.641%   $262.4228   $262.42   $262.40   $262.40  
  Purchase #5 $154.69   12.474%   $173.986   $173.99   $174.00   $174.00  
  Purchase #6 $37.59   10.210%   $41.4279   $41.43   $41.45   $41.40  
  Purchase #7 $184.73   13.701%   $210.0399   $210.04   $210.05   $210.00  
  7 purchase totals = $825.15       $905.9912   $905.99   $906.00   $905.90