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 $59.79   10.303%   $65.9502   $65.95   $65.95   $66.00  
  Purchase #2 $220.78   13.533%   $250.6582   $250.66   $250.65   $250.70  
  Purchase #3 $234.37   11.540%   $261.4163   $261.42   $261.40   $261.40  
  Purchase #4 $80.88   12.793%   $91.227   $91.23   $91.25   $91.20  
  Purchase #5 $196.66   3.661%   $203.8597   $203.86   $203.85   $203.90  
  Purchase #6 $219.33   12.628%   $247.027   $247.03   $247.05   $247.00  
  Purchase #7 $106.57   12.488%   $119.8785   $119.88   $119.90   $119.90  
  7 purchase totals = $1,118.38       $1,240.0169   $1,240.03   $1,240.05   $1,240.10