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	$126.59	9.603%	$138.7464	$138.75	$138.75	$138.70
Purchase #2	$7.26	5.107%	$7.6308	$7.63	$7.65	$7.60
Purchase #3	$197.30	13.308%	$223.5567	$223.56	$223.55	$223.60
Purchase #4	$54.38	9.307%	$59.4411	$59.44	$59.45	$59.40
Purchase #5	$55.80	10.679%	$61.7589	$61.76	$61.75	$61.80
Purchase #6	$11.59	13.133%	$13.1121	$13.11	$13.10	$13.10
Purchase #7	$168.54	3.375%	$174.2282	$174.23	$174.25	$174.20
7 purchase totals =	$621.46		$678.4742	$678.48	$678.50	$678.40