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 $83.41   3.534%   $86.3577   $86.36   $86.35   $86.40  
  Purchase #2 $85.63   7.272%   $91.857   $91.86   $91.85   $91.90  
  Purchase #3 $60.71   10.848%   $67.2958   $67.30   $67.30   $67.30  
  Purchase #4 $150.54   8.774%   $163.7484   $163.75   $163.75   $163.70  
  Purchase #5 $14.71   13.135%   $16.6422   $16.64   $16.65   $16.60  
  Purchase #6 $246.72   4.792%   $258.5428   $258.54   $258.55   $258.50  
  Purchase #7 $62.72   7.138%   $67.197   $67.20   $67.20   $67.20  
  7 purchase totals = $704.44       $751.6409   $751.65   $751.65   $751.60