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	$78.92	5.588%	$83.33	$83.33	$83.35	$83.30
Purchase #2	$139.49	12.176%	$156.4743	$156.47	$156.45	$156.50
Purchase #3	$93.51	4.664%	$97.8713	$97.87	$97.85	$97.90
Purchase #4	$97.48	3.121%	$100.5224	$100.52	$100.50	$100.50
Purchase #5	$175.42	13.518%	$199.1333	$199.13	$199.15	$199.10
Purchase #6	$199.50	3.694%	$206.8695	$206.87	$206.85	$206.90
Purchase #7	$131.99	7.596%	$142.016	$142.02	$142.00	$142.00
7 purchase totals =	$916.31		$986.2168	$986.21	$986.15	$986.20