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	$77.75	6.196%	$82.5674	$82.57	$82.55	$82.60
Purchase #2	$88.84	11.786%	$99.3107	$99.31	$99.30	$99.30
Purchase #3	$66.44	11.268%	$73.9265	$73.93	$73.95	$73.90
Purchase #4	$201.76	5.368%	$212.5905	$212.59	$212.60	$212.60
Purchase #5	$18.66	7.513%	$20.0619	$20.06	$20.05	$20.10
Purchase #6	$47.73	7.570%	$51.3432	$51.34	$51.35	$51.30
Purchase #7	$166.59	8.515%	$180.7751	$180.78	$180.80	$180.80
7 purchase totals =	$667.77		$720.5753	$720.58	$720.60	$720.60