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	$62.90	5.700%	$66.4853	$66.49	$66.50	$66.50
Purchase #2	$55.39	11.779%	$61.9144	$61.91	$61.90	$61.90
Purchase #3	$12.46	6.658%	$13.2896	$13.29	$13.30	$13.30
Purchase #4	$151.73	3.268%	$156.6885	$156.69	$156.70	$156.70
Purchase #5	$209.29	6.686%	$223.2831	$223.28	$223.30	$223.30
Purchase #6	$65.77	6.846%	$70.2726	$70.27	$70.25	$70.30
Purchase #7	$36.38	6.413%	$38.713	$38.71	$38.70	$38.70
7 purchase totals =	$593.92		$630.6465	$630.64	$630.65	$630.70