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	$65.41	13.802%	$74.4379	$74.44	$74.45	$74.40
Purchase #2	$176.71	13.214%	$200.0605	$200.06	$200.05	$200.10
Purchase #3	$77.71	4.158%	$80.9412	$80.94	$80.95	$80.90
Purchase #4	$7.59	11.120%	$8.434	$8.43	$8.45	$8.40
Purchase #5	$59.43	13.199%	$67.2742	$67.27	$67.25	$67.30
Purchase #6	$130.82	13.570%	$148.5723	$148.57	$148.55	$148.60
Purchase #7	$124.97	6.519%	$133.1168	$133.12	$133.10	$133.10
7 purchase totals =	$642.64		$712.8369	$712.83	$712.80	$712.80