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	$159.82	7.391%	$171.6323	$171.63	$171.65	$171.60
Purchase #2	$97.36	12.585%	$109.6128	$109.61	$109.60	$109.60
Purchase #3	$105.48	5.825%	$111.6242	$111.62	$111.60	$111.60
Purchase #4	$227.32	3.759%	$235.865	$235.87	$235.85	$235.90
Purchase #5	$124.96	13.448%	$141.7646	$141.76	$141.75	$141.80
Purchase #6	$57.88	3.230%	$59.7495	$59.75	$59.75	$59.70
Purchase #7	$130.45	7.139%	$139.7628	$139.76	$139.75	$139.80
7 purchase totals =	$903.27		$970.0112	$970.00	$969.95	$970.00