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 $97.65   10.541%   $107.9433   $107.94   $107.95   $107.90  
  Purchase #2 $10.30   5.393%   $10.8555   $10.86   $10.85   $10.90  
  Purchase #3 $72.91   13.417%   $82.6923   $82.69   $82.70   $82.70  
  Purchase #4 $53.33   13.248%   $60.3952   $60.40   $60.40   $60.40  
  Purchase #5 $24.86   10.242%   $27.4062   $27.41   $27.40   $27.40  
  Purchase #6 $233.32   8.502%   $253.1569   $253.16   $253.15   $253.20  
  Purchase #7 $231.90   13.853%   $264.0251   $264.03   $264.05   $264.00  
  7 purchase totals = $724.27       $806.4745   $806.49   $806.50   $806.50