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	$67.85	5.819%	$71.7982	$71.80	$71.80	$71.80
Purchase #2	$131.74	12.470%	$148.168	$148.17	$148.15	$148.20
Purchase #3	$92.25	13.853%	$105.0294	$105.03	$105.05	$105.00
Purchase #4	$136.55	10.466%	$150.8413	$150.84	$150.85	$150.80
Purchase #5	$28.71	7.337%	$30.8165	$30.82	$30.80	$30.80
Purchase #6	$176.51	13.487%	$200.3159	$200.32	$200.30	$200.30
Purchase #7	$50.51	9.835%	$55.4777	$55.48	$55.50	$55.50
7 purchase totals =	$684.12		$762.4470	$762.46	$762.45	$762.40