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 $224.85   7.608%   $241.9566   $241.96   $241.95   $242.00  
  Purchase #2 $244.53   13.291%   $277.0305   $277.03   $277.05   $277.00  
  Purchase #3 $167.37   13.746%   $190.3767   $190.38   $190.40   $190.40  
  Purchase #4 $240.30   3.117%   $247.7902   $247.79   $247.80   $247.80  
  Purchase #5 $247.71   7.658%   $266.6796   $266.68   $266.70   $266.70  
  Purchase #6 $34.70   10.676%   $38.4046   $38.40   $38.40   $38.40  
  Purchase #7 $145.76   11.276%   $162.1959   $162.20   $162.20   $162.20  
  7 purchase totals = $1,305.22       $1,424.4341   $1,424.44   $1,424.50   $1,424.50