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	$85.29	5.275%	$89.789	$89.79	$89.80	$89.80
Purchase #2	$231.25	13.229%	$261.8421	$261.84	$261.85	$261.80
Purchase #3	$180.51	12.662%	$203.3662	$203.37	$203.35	$203.40
Purchase #4	$191.51	5.216%	$201.4992	$201.50	$201.50	$201.50
Purchase #5	$186.27	6.500%	$198.3776	$198.38	$198.40	$198.40
Purchase #6	$86.83	3.794%	$90.1243	$90.12	$90.10	$90.10
Purchase #7	$104.42	12.352%	$117.318	$117.32	$117.30	$117.30
7 purchase totals =	$1,066.08		$1,162.3164	$1,162.32	$1,162.30	$1,162.30