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	$132.45	6.442%	$140.9824	$140.98	$141.00	$141.00
Purchase #2	$147.85	10.118%	$162.8095	$162.81	$162.80	$162.80
Purchase #3	$95.78	12.825%	$108.0638	$108.06	$108.05	$108.10
Purchase #4	$135.50	3.612%	$140.3943	$140.39	$140.40	$140.40
Purchase #5	$128.69	7.628%	$138.5065	$138.51	$138.50	$138.50
Purchase #6	$100.53	4.565%	$105.1192	$105.12	$105.10	$105.10
Purchase #7	$247.72	9.813%	$272.0288	$272.03	$272.05	$272.00
7 purchase totals =	$988.52		$1,067.9045	$1,067.90	$1,067.90	$1,067.90