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	$120.54	8.692%	$131.0173	$131.02	$131.00	$131.00
Purchase #2	$87.77	13.153%	$99.3144	$99.31	$99.30	$99.30
Purchase #3	$67.84	7.847%	$73.1634	$73.16	$73.15	$73.20
Purchase #4	$202.31	9.422%	$221.3716	$221.37	$221.35	$221.40
Purchase #5	$105.64	10.513%	$116.7459	$116.75	$116.75	$116.70
Purchase #6	$81.27	10.760%	$90.0147	$90.01	$90.00	$90.00
Purchase #7	$109.29	13.802%	$124.3742	$124.37	$124.35	$124.40
7 purchase totals =	$774.66		$856.0015	$855.99	$855.90	$856.00