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	$45.38	11.207%	$50.4657	$50.47	$50.45	$50.50
Purchase #2	$61.82	13.738%	$70.3128	$70.31	$70.30	$70.30
Purchase #3	$181.28	13.313%	$205.4138	$205.41	$205.40	$205.40
Purchase #4	$163.60	13.271%	$185.3114	$185.31	$185.30	$185.30
Purchase #5	$185.82	8.631%	$201.8581	$201.86	$201.85	$201.90
Purchase #6	$145.56	7.436%	$156.3838	$156.38	$156.40	$156.40
Purchase #7	$167.72	6.869%	$179.2407	$179.24	$179.25	$179.20
7 purchase totals =	$951.18		$1,048.9863	$1,048.98	$1,048.95	$1,049.00