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	$145.40	10.250%	$160.3035	$160.30	$160.30	$160.30
Purchase #2	$52.29	7.616%	$56.2724	$56.27	$56.25	$56.30
Purchase #3	$21.95	4.250%	$22.8829	$22.88	$22.90	$22.90
Purchase #4	$66.74	6.853%	$71.3137	$71.31	$71.30	$71.30
Purchase #5	$118.82	4.566%	$124.2453	$124.25	$124.25	$124.20
Purchase #6	$78.28	6.869%	$83.6571	$83.66	$83.65	$83.70
Purchase #7	$115.57	6.657%	$123.2635	$123.26	$123.25	$123.30
7 purchase totals =	$599.05		$641.9384	$641.93	$641.90	$642.00