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	$238.83	3.794%	$247.8912	$247.89	$247.90	$247.90
Purchase #2	$40.90	11.450%	$45.5831	$45.58	$45.60	$45.60
Purchase #3	$222.84	12.281%	$250.207	$250.21	$250.20	$250.20
Purchase #4	$216.32	5.328%	$227.8455	$227.85	$227.85	$227.80
Purchase #5	$89.79	3.130%	$92.6004	$92.60	$92.60	$92.60
Purchase #6	$134.93	9.429%	$147.6525	$147.65	$147.65	$147.70
Purchase #7	$16.90	10.602%	$18.6917	$18.69	$18.70	$18.70
7 purchase totals =	$960.51		$1,030.4714	$1,030.47	$1,030.50	$1,030.50