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	$66.95	8.658%	$72.7465	$72.75	$72.75	$72.70
Purchase #2	$191.39	9.240%	$209.0744	$209.07	$209.05	$209.10
Purchase #3	$12.92	5.349%	$13.6111	$13.61	$13.60	$13.60
Purchase #4	$87.89	12.190%	$98.6038	$98.60	$98.60	$98.60
Purchase #5	$20.92	6.773%	$22.3369	$22.34	$22.35	$22.30
Purchase #6	$134.25	13.355%	$152.1791	$152.18	$152.20	$152.20
Purchase #7	$133.59	10.272%	$147.3124	$147.31	$147.30	$147.30
7 purchase totals =	$647.91		$715.8642	$715.86	$715.85	$715.80