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	$129.76	3.296%	$134.0369	$134.04	$134.05	$134.00
Purchase #2	$56.67	5.495%	$59.784	$59.78	$59.80	$59.80
Purchase #3	$92.39	7.759%	$99.5585	$99.56	$99.55	$99.60
Purchase #4	$239.29	3.334%	$247.2679	$247.27	$247.25	$247.30
Purchase #5	$107.75	11.560%	$120.2059	$120.21	$120.20	$120.20
Purchase #6	$197.35	6.466%	$210.1107	$210.11	$210.10	$210.10
Purchase #7	$105.68	3.310%	$109.178	$109.18	$109.20	$109.20
7 purchase totals =	$928.89		$980.1419	$980.15	$980.15	$980.20