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	$162.73	3.739%	$168.8145	$168.81	$168.80	$168.80
Purchase #2	$99.32	6.360%	$105.6368	$105.64	$105.65	$105.60
Purchase #3	$7.94	9.267%	$8.6758	$8.68	$8.70	$8.70
Purchase #4	$164.45	3.571%	$170.3225	$170.32	$170.30	$170.30
Purchase #5	$100.65	13.565%	$114.3032	$114.30	$114.30	$114.30
Purchase #6	$28.67	9.814%	$31.4837	$31.48	$31.50	$31.50
Purchase #7	$75.88	3.508%	$78.5419	$78.54	$78.55	$78.50
7 purchase totals =	$639.64		$677.7784	$677.77	$677.80	$677.70