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	$37.40	6.474%	$39.8213	$39.82	$39.80	$39.80
Purchase #2	$114.31	3.352%	$118.1417	$118.14	$118.15	$118.10
Purchase #3	$221.68	13.117%	$250.7578	$250.76	$250.75	$250.80
Purchase #4	$132.53	11.178%	$147.3442	$147.34	$147.35	$147.30
Purchase #5	$231.32	8.258%	$250.4224	$250.42	$250.40	$250.40
Purchase #6	$229.79	4.393%	$239.8847	$239.88	$239.90	$239.90
Purchase #7	$93.86	3.288%	$96.9461	$96.95	$96.95	$96.90
7 purchase totals =	$1,060.89		$1,143.3182	$1,143.31	$1,143.30	$1,143.20