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	$72.91	8.121%	$78.831	$78.83	$78.85	$78.80
Purchase #2	$124.66	13.423%	$141.3931	$141.39	$141.40	$141.40
Purchase #3	$81.90	13.428%	$92.8975	$92.90	$92.90	$92.90
Purchase #4	$97.74	4.788%	$102.4198	$102.42	$102.40	$102.40
Purchase #5	$155.83	3.169%	$160.7683	$160.77	$160.75	$160.80
Purchase #6	$91.96	12.318%	$103.2876	$103.29	$103.30	$103.30
Purchase #7	$30.88	4.178%	$32.1702	$32.17	$32.15	$32.20
7 purchase totals =	$655.88		$711.7675	$711.77	$711.75	$711.80