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	$25.28	9.236%	$27.6149	$27.61	$27.60	$27.60
Purchase #2	$182.65	6.520%	$194.5588	$194.56	$194.55	$194.60
Purchase #3	$74.53	11.104%	$82.8058	$82.81	$82.80	$82.80
Purchase #4	$82.49	13.347%	$93.4999	$93.50	$93.50	$93.50
Purchase #5	$203.85	7.664%	$219.4731	$219.47	$219.45	$219.50
Purchase #6	$39.42	7.397%	$42.3359	$42.34	$42.35	$42.30
Purchase #7	$133.39	9.707%	$146.3382	$146.34	$146.35	$146.30
7 purchase totals =	$741.61		$806.6266	$806.63	$806.60	$806.60