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	$28.49	8.120%	$30.8034	$30.80	$30.80	$30.80
Purchase #2	$13.47	7.521%	$14.4831	$14.48	$14.50	$14.50
Purchase #3	$127.82	11.316%	$142.2841	$142.28	$142.30	$142.30
Purchase #4	$226.46	7.450%	$243.3313	$243.33	$243.35	$243.30
Purchase #5	$142.86	4.866%	$149.8116	$149.81	$149.80	$149.80
Purchase #6	$43.89	3.759%	$45.5398	$45.54	$45.55	$45.50
Purchase #7	$146.73	13.495%	$166.5312	$166.53	$166.55	$166.50
7 purchase totals =	$729.72		$792.7845	$792.77	$792.85	$792.70