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	$147.46	13.363%	$167.1651	$167.17	$167.15	$167.20
Purchase #2	$176.66	11.418%	$196.831	$196.83	$196.85	$196.80
Purchase #3	$242.56	5.439%	$255.7528	$255.75	$255.75	$255.80
Purchase #4	$97.35	13.614%	$110.6032	$110.60	$110.60	$110.60
Purchase #5	$17.85	13.784%	$20.3104	$20.31	$20.30	$20.30
Purchase #6	$204.32	9.790%	$224.3229	$224.32	$224.30	$224.30
Purchase #7	$22.60	9.619%	$24.7739	$24.77	$24.75	$24.80
7 purchase totals =	$908.80		$999.7593	$999.75	$999.70	$999.80