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	$17.28	5.399%	$18.2129	$18.21	$18.20	$18.20
Purchase #2	$180.76	5.586%	$190.8573	$190.86	$190.85	$190.90
Purchase #3	$90.28	6.474%	$96.1247	$96.12	$96.10	$96.10
Purchase #4	$85.82	4.510%	$89.6905	$89.69	$89.70	$89.70
Purchase #5	$56.46	11.329%	$62.8564	$62.86	$62.85	$62.90
Purchase #6	$105.52	13.763%	$120.0427	$120.04	$120.05	$120.00
Purchase #7	$15.80	9.812%	$17.3503	$17.35	$17.35	$17.40
7 purchase totals =	$551.92		$595.1348	$595.13	$595.10	$595.20