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	$73.63	3.420%	$76.1481	$76.15	$76.15	$76.10
Purchase #2	$50.75	7.611%	$54.6126	$54.61	$54.60	$54.60
Purchase #3	$195.73	13.605%	$222.3591	$222.36	$222.35	$222.40
Purchase #4	$126.28	8.517%	$137.0353	$137.04	$137.05	$137.00
Purchase #5	$22.31	13.400%	$25.2995	$25.30	$25.30	$25.30
Purchase #6	$41.34	13.354%	$46.8605	$46.86	$46.85	$46.90
Purchase #7	$120.86	5.611%	$127.6415	$127.64	$127.65	$127.60
7 purchase totals =	$630.90		$689.9566	$689.96	$689.95	$689.90