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	$130.95	11.374%	$145.8443	$145.84	$145.85	$145.80
Purchase #2	$40.57	3.871%	$42.1405	$42.14	$42.15	$42.10
Purchase #3	$167.74	6.679%	$178.9434	$178.94	$178.95	$178.90
Purchase #4	$124.70	9.276%	$136.2672	$136.27	$136.25	$136.30
Purchase #5	$238.88	8.220%	$258.5159	$258.52	$258.50	$258.50
Purchase #6	$87.64	4.451%	$91.5409	$91.54	$91.55	$91.50
Purchase #7	$139.74	5.414%	$147.3055	$147.31	$147.30	$147.30
7 purchase totals =	$930.22		$1,000.5577	$1,000.56	$1,000.55	$1,000.40