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	$16.43	11.682%	$18.3494	$18.35	$18.35	$18.30
Purchase #2	$26.97	5.194%	$28.3708	$28.37	$28.35	$28.40
Purchase #3	$160.34	13.229%	$181.5514	$181.55	$181.55	$181.60
Purchase #4	$83.61	7.676%	$90.0279	$90.03	$90.05	$90.00
Purchase #5	$130.65	6.399%	$139.0103	$139.01	$139.00	$139.00
Purchase #6	$157.55	9.582%	$172.6464	$172.65	$172.65	$172.60
Purchase #7	$55.53	10.312%	$61.2563	$61.26	$61.25	$61.30
7 purchase totals =	$631.08		$691.2125	$691.22	$691.20	$691.20