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	$26.32	7.547%	$28.3064	$28.31	$28.30	$28.30
Purchase #2	$238.43	8.675%	$259.1138	$259.11	$259.10	$259.10
Purchase #3	$21.61	9.110%	$23.5787	$23.58	$23.60	$23.60
Purchase #4	$55.48	6.677%	$59.1844	$59.18	$59.20	$59.20
Purchase #5	$43.48	4.366%	$45.3783	$45.38	$45.40	$45.40
Purchase #6	$186.73	6.686%	$199.2148	$199.21	$199.20	$199.20
Purchase #7	$223.37	13.718%	$254.0119	$254.01	$254.00	$254.00
7 purchase totals =	$795.42		$868.7883	$868.78	$868.80	$868.80