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	$29.42	4.745%	$30.816	$30.82	$30.80	$30.80
Purchase #2	$40.50	4.127%	$42.1714	$42.17	$42.15	$42.20
Purchase #3	$134.73	8.115%	$145.6633	$145.66	$145.65	$145.70
Purchase #4	$158.82	6.268%	$168.7748	$168.77	$168.75	$168.80
Purchase #5	$36.57	12.539%	$41.1555	$41.16	$41.15	$41.20
Purchase #6	$196.36	13.739%	$223.3379	$223.34	$223.35	$223.30
Purchase #7	$87.82	11.211%	$97.6655	$97.67	$97.65	$97.70
7 purchase totals =	$684.22		$749.5844	$749.59	$749.50	$749.70