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	$17.28	4.861%	$18.12	$18.12	$18.10	$18.10
Purchase #2	$200.47	9.323%	$219.1598	$219.16	$219.15	$219.20
Purchase #3	$174.79	4.348%	$182.3899	$182.39	$182.40	$182.40
Purchase #4	$125.66	13.264%	$142.3275	$142.33	$142.35	$142.30
Purchase #5	$73.85	13.462%	$83.7917	$83.79	$83.80	$83.80
Purchase #6	$134.46	12.666%	$151.4907	$151.49	$151.50	$151.50
Purchase #7	$7.50	3.740%	$7.7805	$7.78	$7.80	$7.80
7 purchase totals =	$734.01		$805.0601	$805.06	$805.10	$805.10