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	$93.39	5.579%	$98.6002	$98.60	$98.60	$98.60
Purchase #2	$98.56	3.414%	$101.9248	$101.92	$101.90	$101.90
Purchase #3	$218.57	13.117%	$247.2398	$247.24	$247.25	$247.20
Purchase #4	$159.40	11.650%	$177.9701	$177.97	$177.95	$178.00
Purchase #5	$39.83	6.797%	$42.5372	$42.54	$42.55	$42.50
Purchase #6	$34.43	7.143%	$36.8893	$36.89	$36.90	$36.90
Purchase #7	$92.42	4.493%	$96.5724	$96.57	$96.55	$96.60
7 purchase totals =	$736.60		$801.7338	$801.73	$801.70	$801.70