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	$233.38	9.424%	$255.3737	$255.37	$255.35	$255.40
Purchase #2	$28.46	10.344%	$31.4039	$31.40	$31.40	$31.40
Purchase #3	$188.98	9.494%	$206.9218	$206.92	$206.90	$206.90
Purchase #4	$30.72	6.198%	$32.624	$32.62	$32.60	$32.60
Purchase #5	$89.61	10.274%	$98.8165	$98.82	$98.80	$98.80
Purchase #6	$238.60	13.156%	$269.9902	$269.99	$270.00	$270.00
Purchase #7	$74.75	11.867%	$83.6206	$83.62	$83.60	$83.60
7 purchase totals =	$884.50		$978.7507	$978.74	$978.65	$978.70