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	$7.43	4.599%	$7.7717	$7.77	$7.75	$7.80
Purchase #2	$189.73	10.387%	$209.4373	$209.44	$209.45	$209.40
Purchase #3	$34.38	8.803%	$37.4065	$37.41	$37.40	$37.40
Purchase #4	$62.35	13.719%	$70.9038	$70.90	$70.90	$70.90
Purchase #5	$82.51	12.347%	$92.6975	$92.70	$92.70	$92.70
Purchase #6	$85.49	4.305%	$89.1703	$89.17	$89.15	$89.20
Purchase #7	$121.62	6.843%	$129.9425	$129.94	$129.95	$129.90
7 purchase totals =	$583.51		$637.3296	$637.33	$637.30	$637.30