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	$229.77	4.388%	$239.8523	$239.85	$239.85	$239.90
Purchase #2	$226.37	9.613%	$248.1309	$248.13	$248.15	$248.10
Purchase #3	$142.64	5.180%	$150.0288	$150.03	$150.05	$150.00
Purchase #4	$240.30	12.594%	$270.5634	$270.56	$270.55	$270.60
Purchase #5	$184.30	11.107%	$204.7702	$204.77	$204.75	$204.80
Purchase #6	$59.88	3.361%	$61.8926	$61.89	$61.90	$61.90
Purchase #7	$202.49	10.580%	$223.9134	$223.91	$223.90	$223.90
7 purchase totals =	$1,285.75		$1,399.1516	$1,399.14	$1,399.15	$1,399.20