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	$123.72	10.306%	$136.4706	$136.47	$136.45	$136.50
Purchase #2	$101.51	8.708%	$110.3495	$110.35	$110.35	$110.30
Purchase #3	$48.96	8.178%	$52.9639	$52.96	$52.95	$53.00
Purchase #4	$18.55	11.437%	$20.6716	$20.67	$20.65	$20.70
Purchase #5	$82.74	4.612%	$86.556	$86.56	$86.55	$86.60
Purchase #6	$50.90	13.207%	$57.6224	$57.62	$57.60	$57.60
Purchase #7	$174.48	12.701%	$196.6407	$196.64	$196.65	$196.60
7 purchase totals =	$600.86		$661.2747	$661.27	$661.20	$661.30