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	$226.35	10.842%	$250.8909	$250.89	$250.90	$250.90
Purchase #2	$33.95	9.565%	$37.1973	$37.20	$37.20	$37.20
Purchase #3	$102.98	12.595%	$115.9503	$115.95	$115.95	$116.00
Purchase #4	$83.71	7.453%	$89.9489	$89.95	$89.95	$89.90
Purchase #5	$16.77	11.755%	$18.7413	$18.74	$18.75	$18.70
Purchase #6	$80.69	5.562%	$85.178	$85.18	$85.20	$85.20
Purchase #7	$231.32	3.104%	$238.5002	$238.50	$238.50	$238.50
7 purchase totals =	$775.77		$836.4069	$836.41	$836.45	$836.40