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	$100.91	13.155%	$114.1847	$114.18	$114.20	$114.20
Purchase #2	$39.78	7.406%	$42.7261	$42.73	$42.75	$42.70
Purchase #3	$219.60	12.291%	$246.591	$246.59	$246.60	$246.60
Purchase #4	$75.79	10.253%	$83.5607	$83.56	$83.55	$83.60
Purchase #5	$200.39	7.601%	$215.6216	$215.62	$215.60	$215.60
Purchase #6	$224.80	12.597%	$253.1181	$253.12	$253.10	$253.10
Purchase #7	$249.25	10.339%	$275.02	$275.02	$275.00	$275.00
7 purchase totals =	$1,110.52		$1,230.8222	$1,230.82	$1,230.80	$1,230.80