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	$223.66	12.599%	$251.8389	$251.84	$251.85	$251.80
Purchase #2	$122.51	6.498%	$130.4707	$130.47	$130.45	$130.50
Purchase #3	$26.37	5.541%	$27.8312	$27.83	$27.85	$27.80
Purchase #4	$96.29	9.474%	$105.4125	$105.41	$105.40	$105.40
Purchase #5	$53.32	12.375%	$59.9184	$59.92	$59.90	$59.90
Purchase #6	$166.47	7.563%	$179.0601	$179.06	$179.05	$179.10
Purchase #7	$9.83	7.696%	$10.5865	$10.59	$10.60	$10.60
7 purchase totals =	$698.45		$765.1183	$765.12	$765.10	$765.10