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	$200.75	8.586%	$217.9864	$217.99	$218.00	$218.00
Purchase #2	$227.41	10.131%	$250.4489	$250.45	$250.45	$250.40
Purchase #3	$157.74	3.208%	$162.8003	$162.80	$162.80	$162.80
Purchase #4	$17.81	3.590%	$18.4494	$18.45	$18.45	$18.40
Purchase #5	$38.86	11.753%	$43.4272	$43.43	$43.45	$43.40
Purchase #6	$174.28	3.483%	$180.3502	$180.35	$180.35	$180.40
Purchase #7	$83.48	7.870%	$90.0499	$90.05	$90.05	$90.00
7 purchase totals =	$900.33		$963.5123	$963.52	$963.55	$963.40