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	$170.48	8.592%	$185.1276	$185.13	$185.15	$185.10
Purchase #2	$246.61	4.573%	$257.8875	$257.89	$257.90	$257.90
Purchase #3	$98.58	11.102%	$109.5244	$109.52	$109.50	$109.50
Purchase #4	$231.54	4.734%	$242.5011	$242.50	$242.50	$242.50
Purchase #5	$224.82	8.711%	$244.4041	$244.40	$244.40	$244.40
Purchase #6	$50.79	10.517%	$56.1316	$56.13	$56.15	$56.10
Purchase #7	$71.83	5.254%	$75.6039	$75.60	$75.60	$75.60
7 purchase totals =	$1,094.65		$1,171.1802	$1,171.17	$1,171.20	$1,171.10