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	$109.73	11.701%	$122.5695	$122.57	$122.55	$122.60
Purchase #2	$212.41	11.603%	$237.0559	$237.06	$237.05	$237.10
Purchase #3	$53.89	13.318%	$61.0671	$61.07	$61.05	$61.10
Purchase #4	$145.46	11.267%	$161.849	$161.85	$161.85	$161.80
Purchase #5	$78.60	6.646%	$83.8238	$83.82	$83.80	$83.80
Purchase #6	$139.39	9.427%	$152.5303	$152.53	$152.55	$152.50
Purchase #7	$170.59	8.291%	$184.7336	$184.73	$184.75	$184.70
7 purchase totals =	$910.07		$1,003.6292	$1,003.63	$1,003.60	$1,003.60