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	$94.44	6.764%	$100.8279	$100.83	$100.85	$100.80
Purchase #2	$64.80	5.380%	$68.2862	$68.29	$68.30	$68.30
Purchase #3	$207.80	8.706%	$225.8911	$225.89	$225.90	$225.90
Purchase #4	$117.34	8.541%	$127.362	$127.36	$127.35	$127.40
Purchase #5	$35.74	5.819%	$37.8197	$37.82	$37.80	$37.80
Purchase #6	$183.66	13.331%	$208.1437	$208.14	$208.15	$208.10
Purchase #7	$17.47	5.311%	$18.3978	$18.40	$18.40	$18.40
7 purchase totals =	$721.25		$786.7284	$786.73	$786.75	$786.70