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	$44.30	3.418%	$45.8142	$45.81	$45.80	$45.80
Purchase #2	$250.37	3.139%	$258.2291	$258.23	$258.25	$258.20
Purchase #3	$164.81	6.246%	$175.104	$175.10	$175.10	$175.10
Purchase #4	$91.54	5.180%	$96.2818	$96.28	$96.30	$96.30
Purchase #5	$32.41	8.832%	$35.2725	$35.27	$35.25	$35.30
Purchase #6	$42.33	7.443%	$45.4806	$45.48	$45.50	$45.50
Purchase #7	$15.86	3.861%	$16.4724	$16.47	$16.45	$16.50
7 purchase totals =	$641.62		$672.6546	$672.64	$672.65	$672.70