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 $24.29   6.821%   $25.9468   $25.95   $25.95   $25.90  
  Purchase #2 $226.99   4.196%   $236.5145   $236.51   $236.50   $236.50  
  Purchase #3 $133.87   11.869%   $149.759   $149.76   $149.75   $149.80  
  Purchase #4 $58.98   10.210%   $65.0019   $65.00   $65.00   $65.00  
  Purchase #5 $85.28   3.563%   $88.3185   $88.32   $88.30   $88.30  
  Purchase #6 $29.31   5.135%   $30.8151   $30.82   $30.80   $30.80  
  Purchase #7 $122.85   6.531%   $130.8733   $130.87   $130.85   $130.90  
  7 purchase totals = $681.57       $727.2291   $727.23   $727.15   $727.20