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	$221.77	12.842%	$250.2497	$250.25	$250.25	$250.20
Purchase #2	$50.47	5.232%	$53.1106	$53.11	$53.10	$53.10
Purchase #3	$131.78	4.567%	$137.7984	$137.80	$137.80	$137.80
Purchase #4	$45.27	12.598%	$50.9731	$50.97	$50.95	$51.00
Purchase #5	$84.30	6.602%	$89.8655	$89.87	$89.85	$89.90
Purchase #6	$145.30	6.713%	$155.054	$155.05	$155.05	$155.10
Purchase #7	$236.46	9.166%	$258.1339	$258.13	$258.15	$258.10
7 purchase totals =	$915.35		$995.1852	$995.18	$995.15	$995.20