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	$78.89	6.378%	$83.9216	$83.92	$83.90	$83.90
Purchase #2	$41.25	6.758%	$44.0377	$44.04	$44.05	$44.00
Purchase #3	$235.68	13.739%	$268.0601	$268.06	$268.05	$268.10
Purchase #4	$54.84	9.256%	$59.916	$59.92	$59.90	$59.90
Purchase #5	$151.61	13.808%	$172.5443	$172.54	$172.55	$172.50
Purchase #6	$17.97	7.588%	$19.3336	$19.33	$19.35	$19.30
Purchase #7	$84.81	8.800%	$92.2733	$92.27	$92.25	$92.30
7 purchase totals =	$665.05		$740.0866	$740.08	$740.05	$740.00