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	$6.92	10.270%	$7.6307	$7.63	$7.65	$7.60
Purchase #2	$230.96	10.411%	$255.0052	$255.01	$255.00	$255.00
Purchase #3	$161.94	11.191%	$180.0627	$180.06	$180.05	$180.10
Purchase #4	$98.97	12.172%	$111.0166	$111.02	$111.00	$111.00
Purchase #5	$120.81	8.692%	$131.3108	$131.31	$131.30	$131.30
Purchase #6	$219.33	12.745%	$247.2836	$247.28	$247.30	$247.30
Purchase #7	$43.50	7.321%	$46.6846	$46.68	$46.70	$46.70
7 purchase totals =	$882.43		$978.9942	$978.99	$979.00	$979.00