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	$122.92	4.367%	$128.2879	$128.29	$128.30	$128.30
Purchase #2	$138.55	12.459%	$155.8119	$155.81	$155.80	$155.80
Purchase #3	$99.73	12.221%	$111.918	$111.92	$111.90	$111.90
Purchase #4	$244.90	11.871%	$273.9721	$273.97	$273.95	$274.00
Purchase #5	$18.34	6.708%	$19.5702	$19.57	$19.55	$19.60
Purchase #6	$50.45	7.424%	$54.1954	$54.20	$54.20	$54.20
Purchase #7	$148.71	7.540%	$159.9227	$159.92	$159.90	$159.90
7 purchase totals =	$823.60		$903.6782	$903.68	$903.60	$903.70