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	$31.56	4.559%	$32.9988	$33.00	$33.00	$33.00
Purchase #2	$39.81	7.521%	$42.8041	$42.80	$42.80	$42.80
Purchase #3	$152.57	5.426%	$160.8484	$160.85	$160.85	$160.80
Purchase #4	$210.98	13.175%	$238.7766	$238.78	$238.80	$238.80
Purchase #5	$179.77	5.528%	$189.7077	$189.71	$189.70	$189.70
Purchase #6	$117.76	8.621%	$127.9121	$127.91	$127.90	$127.90
Purchase #7	$238.52	3.435%	$246.7132	$246.71	$246.70	$246.70
7 purchase totals =	$970.97		$1,039.7609	$1,039.76	$1,039.75	$1,039.70