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	$11.44	12.296%	$12.8467	$12.85	$12.85	$12.80
Purchase #2	$138.40	9.371%	$151.3695	$151.37	$151.35	$151.40
Purchase #3	$93.33	6.264%	$99.1762	$99.18	$99.20	$99.20
Purchase #4	$222.48	6.131%	$236.1202	$236.12	$236.10	$236.10
Purchase #5	$19.41	7.819%	$20.9277	$20.93	$20.95	$20.90
Purchase #6	$103.75	12.440%	$116.6565	$116.66	$116.65	$116.70
Purchase #7	$137.78	12.541%	$155.059	$155.06	$155.05	$155.10
7 purchase totals =	$726.59		$792.1558	$792.17	$792.15	$792.20