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	$236.34	12.346%	$265.5185	$265.52	$265.50	$265.50
Purchase #2	$65.38	7.215%	$70.0972	$70.10	$70.10	$70.10
Purchase #3	$57.25	6.568%	$61.0102	$61.01	$61.00	$61.00
Purchase #4	$238.77	10.803%	$264.5643	$264.56	$264.55	$264.60
Purchase #5	$103.40	5.427%	$109.0115	$109.01	$109.00	$109.00
Purchase #6	$83.99	9.227%	$91.7398	$91.74	$91.75	$91.70
Purchase #7	$99.27	12.174%	$111.3551	$111.36	$111.35	$111.40
7 purchase totals =	$884.40		$973.2966	$973.30	$973.25	$973.30