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 $241.70   13.821%   $275.1054   $275.11   $275.10   $275.10  
  Purchase #2 $56.43   7.144%   $60.4614   $60.46   $60.45   $60.50  
  Purchase #3 $107.69   11.334%   $119.8956   $119.90   $119.90   $119.90  
  Purchase #4 $102.90   4.447%   $107.476   $107.48   $107.50   $107.50  
  Purchase #5 $239.57   8.675%   $260.3527   $260.35   $260.35   $260.40  
  Purchase #6 $50.27   5.845%   $53.2083   $53.21   $53.20   $53.20  
  Purchase #7 $142.82   5.559%   $150.7594   $150.76   $150.75   $150.80  
  7 purchase totals = $941.38       $1,027.2588   $1,027.27   $1,027.25   $1,027.40