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	$19.59	5.745%	$20.7154	$20.72	$20.70	$20.70
Purchase #2	$223.43	8.257%	$241.8786	$241.88	$241.90	$241.90
Purchase #3	$191.63	12.325%	$215.2484	$215.25	$215.25	$215.20
Purchase #4	$158.58	7.165%	$169.9423	$169.94	$169.95	$169.90
Purchase #5	$42.87	5.334%	$45.1567	$45.16	$45.15	$45.20
Purchase #6	$62.60	12.781%	$70.6009	$70.60	$70.60	$70.60
Purchase #7	$136.68	12.202%	$153.3577	$153.36	$153.35	$153.40
7 purchase totals =	$835.38		$916.9000	$916.91	$916.90	$916.90