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	$159.60	3.644%	$165.4158	$165.42	$165.40	$165.40
Purchase #2	$59.97	3.440%	$62.033	$62.03	$62.05	$62.00
Purchase #3	$181.93	5.219%	$191.4249	$191.42	$191.40	$191.40
Purchase #4	$96.53	3.822%	$100.2194	$100.22	$100.20	$100.20
Purchase #5	$246.74	13.319%	$279.6033	$279.60	$279.60	$279.60
Purchase #6	$53.31	9.421%	$58.3323	$58.33	$58.35	$58.30
Purchase #7	$23.31	3.443%	$24.1126	$24.11	$24.10	$24.10
7 purchase totals =	$821.39		$881.1413	$881.13	$881.10	$881.00