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	$170.75	7.661%	$183.8312	$183.83	$183.85	$183.80
Purchase #2	$219.66	13.822%	$250.0214	$250.02	$250.00	$250.00
Purchase #3	$43.68	4.872%	$45.8081	$45.81	$45.80	$45.80
Purchase #4	$164.40	5.175%	$172.9077	$172.91	$172.90	$172.90
Purchase #5	$82.64	10.590%	$91.3916	$91.39	$91.40	$91.40
Purchase #6	$43.83	6.758%	$46.792	$46.79	$46.80	$46.80
Purchase #7	$42.34	6.725%	$45.1874	$45.19	$45.20	$45.20
7 purchase totals =	$767.30		$835.9394	$835.94	$835.95	$835.90