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	$104.32	11.669%	$116.4931	$116.49	$116.50	$116.50
Purchase #2	$123.34	6.429%	$131.2695	$131.27	$131.25	$131.30
Purchase #3	$113.83	13.851%	$129.5966	$129.60	$129.60	$129.60
Purchase #4	$170.61	5.735%	$180.3945	$180.39	$180.40	$180.40
Purchase #5	$239.31	11.566%	$266.9886	$266.99	$267.00	$267.00
Purchase #6	$205.80	13.618%	$233.8258	$233.83	$233.85	$233.80
Purchase #7	$61.69	12.590%	$69.4568	$69.46	$69.45	$69.50
7 purchase totals =	$1,018.90		$1,128.0249	$1,128.03	$1,128.05	$1,128.10