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	$195.34	11.867%	$218.521	$218.52	$218.50	$218.50
Purchase #2	$223.62	3.402%	$231.2276	$231.23	$231.25	$231.20
Purchase #3	$26.81	9.799%	$29.4371	$29.44	$29.45	$29.40
Purchase #4	$88.59	13.613%	$100.6498	$100.65	$100.65	$100.60
Purchase #5	$142.90	6.535%	$152.2385	$152.24	$152.25	$152.20
Purchase #6	$63.50	10.445%	$70.1326	$70.13	$70.15	$70.10
Purchase #7	$42.41	10.362%	$46.8045	$46.80	$46.80	$46.80
7 purchase totals =	$783.17		$849.0111	$849.01	$849.05	$848.80