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	$73.99	5.802%	$78.2829	$78.28	$78.30	$78.30
Purchase #2	$30.78	13.401%	$34.9048	$34.90	$34.90	$34.90
Purchase #3	$170.88	10.768%	$189.2804	$189.28	$189.30	$189.30
Purchase #4	$39.42	5.254%	$41.4911	$41.49	$41.50	$41.50
Purchase #5	$57.72	12.575%	$64.9783	$64.98	$65.00	$65.00
Purchase #6	$152.31	11.713%	$170.1501	$170.15	$170.15	$170.20
Purchase #7	$42.49	4.397%	$44.3583	$44.36	$44.35	$44.40
7 purchase totals =	$567.59		$623.4459	$623.44	$623.50	$623.60