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	$9.92	9.310%	$10.8436	$10.84	$10.85	$10.80
Purchase #2	$216.68	7.610%	$233.1693	$233.17	$233.15	$233.20
Purchase #3	$190.36	7.349%	$204.3496	$204.35	$204.35	$204.30
Purchase #4	$178.36	13.723%	$202.8363	$202.84	$202.85	$202.80
Purchase #5	$100.47	7.312%	$107.8164	$107.82	$107.80	$107.80
Purchase #6	$159.28	5.149%	$167.4813	$167.48	$167.50	$167.50
Purchase #7	$87.27	3.651%	$90.4562	$90.46	$90.45	$90.50
7 purchase totals =	$942.34		$1,016.9527	$1,016.96	$1,016.95	$1,016.90