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	$76.48	8.849%	$83.2477	$83.25	$83.25	$83.20
Purchase #2	$167.63	11.864%	$187.5176	$187.52	$187.50	$187.50
Purchase #3	$174.44	6.379%	$185.5675	$185.57	$185.55	$185.60
Purchase #4	$106.78	13.145%	$120.8162	$120.82	$120.80	$120.80
Purchase #5	$24.86	8.754%	$27.0362	$27.04	$27.05	$27.00
Purchase #6	$191.58	10.343%	$211.3951	$211.40	$211.40	$211.40
Purchase #7	$129.89	12.338%	$145.9158	$145.92	$145.90	$145.90
7 purchase totals =	$871.66		$961.4961	$961.52	$961.45	$961.40