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	$10.78	9.429%	$11.7964	$11.80	$11.80	$11.80
Purchase #2	$145.34	4.430%	$151.7786	$151.78	$151.80	$151.80
Purchase #3	$165.84	3.188%	$171.127	$171.13	$171.15	$171.10
Purchase #4	$56.55	8.809%	$61.5315	$61.53	$61.55	$61.50
Purchase #5	$232.92	10.160%	$256.5847	$256.58	$256.60	$256.60
Purchase #6	$145.86	10.327%	$160.923	$160.92	$160.90	$160.90
Purchase #7	$88.50	9.515%	$96.9208	$96.92	$96.90	$96.90
7 purchase totals =	$845.79		$910.6620	$910.66	$910.70	$910.60