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	$229.69	11.678%	$256.5132	$256.51	$256.50	$256.50
Purchase #2	$49.32	4.188%	$51.3855	$51.39	$51.40	$51.40
Purchase #3	$229.53	4.303%	$239.4067	$239.41	$239.40	$239.40
Purchase #4	$161.67	9.430%	$176.9155	$176.92	$176.90	$176.90
Purchase #5	$136.50	7.608%	$146.8849	$146.88	$146.90	$146.90
Purchase #6	$45.66	13.419%	$51.7871	$51.79	$51.80	$51.80
Purchase #7	$150.42	4.360%	$156.9783	$156.98	$157.00	$157.00
7 purchase totals =	$1,002.79		$1,079.8712	$1,079.88	$1,079.90	$1,079.90