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 $62.86   7.586%   $67.6286   $67.63   $67.65   $67.60  
  Purchase #2 $21.58   13.228%   $24.4346   $24.43   $24.45   $24.40  
  Purchase #3 $21.61   13.383%   $24.5021   $24.50   $24.50   $24.50  
  Purchase #4 $167.86   8.360%   $181.8931   $181.89   $181.90   $181.90  
  Purchase #5 $98.54   5.781%   $104.2366   $104.24   $104.25   $104.20  
  Purchase #6 $111.73   9.666%   $122.5298   $122.53   $122.55   $122.50  
  Purchase #7 $177.99   7.369%   $191.1061   $191.11   $191.10   $191.10  
  7 purchase totals = $662.17       $716.3309   $716.33   $716.40   $716.20