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	$96.26	13.301%	$109.0635	$109.06	$109.05	$109.10
Purchase #2	$94.39	10.622%	$104.4161	$104.42	$104.40	$104.40
Purchase #3	$224.26	8.557%	$243.4499	$243.45	$243.45	$243.40
Purchase #4	$145.85	7.340%	$156.5554	$156.56	$156.55	$156.60
Purchase #5	$159.73	9.515%	$174.9283	$174.93	$174.95	$174.90
Purchase #6	$49.78	10.240%	$54.8775	$54.88	$54.90	$54.90
Purchase #7	$25.69	11.369%	$28.6107	$28.61	$28.60	$28.60
7 purchase totals =	$795.96		$871.9014	$871.91	$871.90	$871.90