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	$77.26	6.274%	$82.1073	$82.11	$82.10	$82.10
Purchase #2	$40.76	11.139%	$45.3003	$45.30	$45.30	$45.30
Purchase #3	$135.93	6.320%	$144.5208	$144.52	$144.50	$144.50
Purchase #4	$236.83	10.166%	$260.9061	$260.91	$260.90	$260.90
Purchase #5	$136.38	3.212%	$140.7605	$140.76	$140.75	$140.80
Purchase #6	$210.56	10.193%	$232.0224	$232.02	$232.00	$232.00
Purchase #7	$164.88	5.455%	$173.8742	$173.87	$173.85	$173.90
7 purchase totals =	$1,002.60		$1,079.4916	$1,079.49	$1,079.40	$1,079.50