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	$137.42	7.610%	$147.8777	$147.88	$147.90	$147.90
Purchase #2	$102.58	11.664%	$114.5449	$114.54	$114.55	$114.50
Purchase #3	$149.88	10.497%	$165.6129	$165.61	$165.60	$165.60
Purchase #4	$109.97	3.816%	$114.1665	$114.17	$114.15	$114.20
Purchase #5	$119.90	4.729%	$125.5701	$125.57	$125.55	$125.60
Purchase #6	$114.33	3.637%	$118.4882	$118.49	$118.50	$118.50
Purchase #7	$68.86	3.341%	$71.1606	$71.16	$71.15	$71.20
7 purchase totals =	$802.94		$857.4209	$857.42	$857.40	$857.50