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	$100.68	9.102%	$109.8439	$109.84	$109.85	$109.80
Purchase #2	$208.51	11.161%	$231.7818	$231.78	$231.80	$231.80
Purchase #3	$194.82	12.539%	$219.2485	$219.25	$219.25	$219.20
Purchase #4	$74.32	10.645%	$82.2314	$82.23	$82.25	$82.20
Purchase #5	$244.85	12.865%	$276.35	$276.35	$276.35	$276.40
Purchase #6	$172.60	3.632%	$178.8688	$178.87	$178.85	$178.90
Purchase #7	$118.52	12.662%	$133.527	$133.53	$133.55	$133.50
7 purchase totals =	$1,114.30		$1,231.8514	$1,231.85	$1,231.90	$1,231.80