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	$89.72	12.378%	$100.8255	$100.83	$100.85	$100.80
Purchase #2	$214.85	13.283%	$243.3885	$243.39	$243.40	$243.40
Purchase #3	$16.50	4.163%	$17.1869	$17.19	$17.20	$17.20
Purchase #4	$55.42	4.439%	$57.8801	$57.88	$57.90	$57.90
Purchase #5	$104.45	11.635%	$116.6028	$116.60	$116.60	$116.60
Purchase #6	$186.82	6.166%	$198.3393	$198.34	$198.35	$198.30
Purchase #7	$55.33	9.393%	$60.5271	$60.53	$60.55	$60.50
7 purchase totals =	$723.09		$794.7502	$794.76	$794.85	$794.70