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 $33.62   6.842%   $35.9203   $35.92   $35.90   $35.90  
  Purchase #2 $95.44   12.776%   $107.6334   $107.63   $107.65   $107.60  
  Purchase #3 $59.81   4.168%   $62.3029   $62.30   $62.30   $62.30  
  Purchase #4 $86.36   12.350%   $97.0255   $97.03   $97.05   $97.00  
  Purchase #5 $50.42   8.749%   $54.8312   $54.83   $54.85   $54.80  
  Purchase #6 $39.82   13.793%   $45.3124   $45.31   $45.30   $45.30  
  Purchase #7 $127.32   5.732%   $134.618   $134.62   $134.60   $134.60  
  7 purchase totals = $492.79       $537.6437   $537.64   $537.65   $537.50