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	$232.76	13.464%	$264.0988	$264.10	$264.10	$264.10
Purchase #2	$91.89	13.339%	$104.1472	$104.15	$104.15	$104.10
Purchase #3	$166.41	13.748%	$189.288	$189.29	$189.30	$189.30
Purchase #4	$52.32	10.653%	$57.8936	$57.89	$57.90	$57.90
Purchase #5	$151.69	8.318%	$164.3076	$164.31	$164.30	$164.30
Purchase #6	$132.45	4.404%	$138.2831	$138.28	$138.30	$138.30
Purchase #7	$20.30	6.742%	$21.6686	$21.67	$21.65	$21.70
7 purchase totals =	$847.82		$939.6869	$939.69	$939.70	$939.70