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	$152.61	3.779%	$158.3771	$158.38	$158.40	$158.40
Purchase #2	$239.90	3.199%	$247.5744	$247.57	$247.55	$247.60
Purchase #3	$171.86	10.783%	$190.3917	$190.39	$190.40	$190.40
Purchase #4	$156.41	10.183%	$172.3372	$172.34	$172.35	$172.30
Purchase #5	$109.80	9.768%	$120.5253	$120.53	$120.55	$120.50
Purchase #6	$55.41	10.243%	$61.0856	$61.09	$61.10	$61.10
Purchase #7	$30.90	12.427%	$34.7399	$34.74	$34.75	$34.70
7 purchase totals =	$916.89		$985.0312	$985.04	$985.10	$985.00