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	$12.37	11.254%	$13.7621	$13.76	$13.75	$13.80
Purchase #2	$164.31	10.715%	$181.9158	$181.92	$181.90	$181.90
Purchase #3	$19.43	8.681%	$21.1167	$21.12	$21.10	$21.10
Purchase #4	$165.70	13.303%	$187.7431	$187.74	$187.75	$187.70
Purchase #5	$86.25	3.530%	$89.2946	$89.29	$89.30	$89.30
Purchase #6	$102.73	6.133%	$109.0304	$109.03	$109.05	$109.00
Purchase #7	$37.67	6.580%	$40.1487	$40.15	$40.15	$40.10
7 purchase totals =	$588.46		$643.0114	$643.01	$643.00	$642.90