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	$64.54	10.232%	$71.1437	$71.14	$71.15	$71.10
Purchase #2	$81.87	9.707%	$89.8171	$89.82	$89.80	$89.80
Purchase #3	$204.41	4.352%	$213.3059	$213.31	$213.30	$213.30
Purchase #4	$59.97	10.360%	$66.1829	$66.18	$66.20	$66.20
Purchase #5	$225.74	13.872%	$257.0547	$257.05	$257.05	$257.10
Purchase #6	$118.53	12.677%	$133.556	$133.56	$133.55	$133.60
Purchase #7	$38.54	5.418%	$40.6281	$40.63	$40.65	$40.60
7 purchase totals =	$793.60		$871.6884	$871.69	$871.70	$871.70