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	$47.83	11.560%	$53.3591	$53.36	$53.35	$53.40
Purchase #2	$134.61	11.648%	$150.2894	$150.29	$150.30	$150.30
Purchase #3	$83.32	6.543%	$88.7716	$88.77	$88.75	$88.80
Purchase #4	$224.55	3.861%	$233.2199	$233.22	$233.20	$233.20
Purchase #5	$150.42	4.863%	$157.7349	$157.73	$157.75	$157.70
Purchase #6	$134.95	4.612%	$141.1739	$141.17	$141.15	$141.20
Purchase #7	$20.66	3.421%	$21.3668	$21.37	$21.35	$21.40
7 purchase totals =	$796.34		$845.9156	$845.91	$845.85	$846.00