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	$142.85	11.510%	$159.292	$159.29	$159.30	$159.30
Purchase #2	$186.84	13.201%	$211.5047	$211.50	$211.50	$211.50
Purchase #3	$139.93	9.742%	$153.562	$153.56	$153.55	$153.60
Purchase #4	$81.82	10.509%	$90.4185	$90.42	$90.40	$90.40
Purchase #5	$148.43	12.512%	$167.0016	$167.00	$167.00	$167.00
Purchase #6	$246.53	7.144%	$264.1421	$264.14	$264.15	$264.10
Purchase #7	$225.39	9.729%	$247.3182	$247.32	$247.30	$247.30
7 purchase totals =	$1,171.79		$1,293.2391	$1,293.23	$1,293.20	$1,293.20