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	$205.37	8.822%	$223.4877	$223.49	$223.50	$223.50
Purchase #2	$50.54	7.731%	$54.4472	$54.45	$54.45	$54.40
Purchase #3	$228.39	4.707%	$239.1403	$239.14	$239.15	$239.10
Purchase #4	$150.99	11.542%	$168.4173	$168.42	$168.40	$168.40
Purchase #5	$233.99	7.444%	$251.4082	$251.41	$251.40	$251.40
Purchase #6	$115.34	10.495%	$127.4449	$127.44	$127.45	$127.40
Purchase #7	$25.97	10.834%	$28.7836	$28.78	$28.80	$28.80
7 purchase totals =	$1,010.59		$1,093.1292	$1,093.13	$1,093.15	$1,093.00