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	$185.82	5.642%	$196.304	$196.30	$196.30	$196.30
Purchase #2	$146.67	12.843%	$165.5068	$165.51	$165.50	$165.50
Purchase #3	$27.56	12.699%	$31.0598	$31.06	$31.05	$31.10
Purchase #4	$195.91	13.319%	$222.0033	$222.00	$222.00	$222.00
Purchase #5	$123.88	5.115%	$130.2165	$130.22	$130.20	$130.20
Purchase #6	$241.72	7.110%	$258.9063	$258.91	$258.90	$258.90
Purchase #7	$156.76	9.844%	$172.1915	$172.19	$172.20	$172.20
7 purchase totals =	$1,078.32		$1,176.1882	$1,176.19	$1,176.15	$1,176.20