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	$123.26	6.543%	$131.3249	$131.32	$131.30	$131.30
Purchase #2	$67.60	4.201%	$70.4399	$70.44	$70.45	$70.40
Purchase #3	$61.65	4.401%	$64.3632	$64.36	$64.35	$64.40
Purchase #4	$27.86	12.175%	$31.252	$31.25	$31.25	$31.30
Purchase #5	$207.42	8.769%	$225.6087	$225.61	$225.60	$225.60
Purchase #6	$127.46	4.762%	$133.5296	$133.53	$133.55	$133.50
Purchase #7	$19.43	8.215%	$21.0262	$21.03	$21.05	$21.00
7 purchase totals =	$634.68		$677.5445	$677.54	$677.55	$677.50