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	$156.35	11.489%	$174.3131	$174.31	$174.30	$174.30
Purchase #2	$43.78	12.787%	$49.3781	$49.38	$49.40	$49.40
Purchase #3	$146.59	3.805%	$152.1677	$152.17	$152.15	$152.20
Purchase #4	$204.67	8.361%	$221.7825	$221.78	$221.80	$221.80
Purchase #5	$52.77	10.302%	$58.2064	$58.21	$58.20	$58.20
Purchase #6	$116.27	10.514%	$128.4946	$128.49	$128.50	$128.50
Purchase #7	$54.55	9.481%	$59.7219	$59.72	$59.70	$59.70
7 purchase totals =	$774.98		$844.0643	$844.06	$844.05	$844.10