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	$40.90	10.844%	$45.3352	$45.34	$45.35	$45.30
Purchase #2	$41.91	7.325%	$44.9799	$44.98	$45.00	$45.00
Purchase #3	$49.31	12.521%	$55.4841	$55.48	$55.50	$55.50
Purchase #4	$244.49	4.119%	$254.5605	$254.56	$254.55	$254.60
Purchase #5	$156.37	6.715%	$166.8702	$166.87	$166.85	$166.90
Purchase #6	$18.49	4.532%	$19.328	$19.33	$19.35	$19.30
Purchase #7	$157.50	6.337%	$167.4808	$167.48	$167.50	$167.50
7 purchase totals =	$708.97		$754.0387	$754.04	$754.10	$754.10