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	$36.40	7.612%	$39.1708	$39.17	$39.15	$39.20
Purchase #2	$248.43	6.327%	$264.1482	$264.15	$264.15	$264.10
Purchase #3	$211.43	9.665%	$231.8647	$231.86	$231.85	$231.90
Purchase #4	$76.67	4.113%	$79.8234	$79.82	$79.80	$79.80
Purchase #5	$112.33	13.205%	$127.1632	$127.16	$127.15	$127.20
Purchase #6	$17.81	3.183%	$18.3769	$18.38	$18.40	$18.40
Purchase #7	$168.48	4.255%	$175.6488	$175.65	$175.65	$175.60
7 purchase totals =	$871.55		$936.1960	$936.19	$936.15	$936.20