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	$159.39	3.429%	$164.8555	$164.86	$164.85	$164.90
Purchase #2	$59.93	4.123%	$62.4009	$62.40	$62.40	$62.40
Purchase #3	$197.76	11.578%	$220.6567	$220.66	$220.65	$220.70
Purchase #4	$194.98	13.461%	$221.2263	$221.23	$221.25	$221.20
Purchase #5	$119.32	5.450%	$125.8229	$125.82	$125.80	$125.80
Purchase #6	$56.67	13.234%	$64.1697	$64.17	$64.15	$64.20
Purchase #7	$172.51	4.525%	$180.3161	$180.32	$180.30	$180.30
7 purchase totals =	$960.56		$1,039.4481	$1,039.46	$1,039.40	$1,039.50