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	$52.79	4.719%	$55.2812	$55.28	$55.30	$55.30
Purchase #2	$79.48	6.128%	$84.3505	$84.35	$84.35	$84.40
Purchase #3	$171.66	11.403%	$191.2344	$191.23	$191.25	$191.20
Purchase #4	$142.48	5.543%	$150.3777	$150.38	$150.40	$150.40
Purchase #5	$28.71	13.596%	$32.6134	$32.61	$32.60	$32.60
Purchase #6	$80.85	13.718%	$91.941	$91.94	$91.95	$91.90
Purchase #7	$244.68	4.454%	$255.578	$255.58	$255.60	$255.60
7 purchase totals =	$800.65		$861.3762	$861.37	$861.45	$861.40