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	$42.72	6.216%	$45.3755	$45.38	$45.40	$45.40
Purchase #2	$18.47	10.580%	$20.4241	$20.42	$20.40	$20.40
Purchase #3	$175.60	10.824%	$194.6069	$194.61	$194.60	$194.60
Purchase #4	$210.52	12.401%	$236.6266	$236.63	$236.65	$236.60
Purchase #5	$145.66	13.475%	$165.2877	$165.29	$165.30	$165.30
Purchase #6	$240.80	10.560%	$266.2285	$266.23	$266.25	$266.20
Purchase #7	$193.32	12.239%	$216.9804	$216.98	$217.00	$217.00
7 purchase totals =	$1,027.09		$1,145.5297	$1,145.54	$1,145.60	$1,145.50