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	$172.73	7.419%	$185.5448	$185.54	$185.55	$185.50
Purchase #2	$189.84	12.233%	$213.0631	$213.06	$213.05	$213.10
Purchase #3	$72.94	12.738%	$82.2311	$82.23	$82.25	$82.20
Purchase #4	$231.85	10.423%	$256.0157	$256.02	$256.00	$256.00
Purchase #5	$79.56	5.263%	$83.7472	$83.75	$83.75	$83.70
Purchase #6	$37.42	10.346%	$41.2915	$41.29	$41.30	$41.30
Purchase #7	$245.54	9.789%	$269.5759	$269.58	$269.60	$269.60
7 purchase totals =	$1,029.88		$1,131.4693	$1,131.47	$1,131.50	$1,131.40