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 $32.90   5.355%   $34.6618   $34.66   $34.65   $34.70  
  Purchase #2 $191.47   8.402%   $207.5573   $207.56   $207.55   $207.60  
  Purchase #3 $21.44   7.763%   $23.1044   $23.10   $23.10   $23.10  
  Purchase #4 $157.78   3.510%   $163.3181   $163.32   $163.30   $163.30  
  Purchase #5 $68.40   7.439%   $73.4883   $73.49   $73.50   $73.50  
  Purchase #6 $82.84   10.332%   $91.399   $91.40   $91.40   $91.40  
  Purchase #7 $241.91   4.814%   $253.5555   $253.56   $253.55   $253.60  
  7 purchase totals = $796.74       $847.0844   $847.09   $847.05   $847.20