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	$142.94	4.585%	$149.4938	$149.49	$149.50	$149.50
Purchase #2	$78.59	7.267%	$84.3011	$84.30	$84.30	$84.30
Purchase #3	$53.70	10.627%	$59.4067	$59.41	$59.40	$59.40
Purchase #4	$60.94	9.554%	$66.7622	$66.76	$66.75	$66.80
Purchase #5	$175.41	13.365%	$198.8535	$198.85	$198.85	$198.90
Purchase #6	$58.89	10.805%	$65.2531	$65.25	$65.25	$65.30
Purchase #7	$61.95	5.753%	$65.514	$65.51	$65.50	$65.50
7 purchase totals =	$632.42		$689.5844	$689.57	$689.55	$689.70