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	$52.72	12.330%	$59.2204	$59.22	$59.20	$59.20
Purchase #2	$237.56	5.257%	$250.0485	$250.05	$250.05	$250.00
Purchase #3	$88.54	13.622%	$100.6009	$100.60	$100.60	$100.60
Purchase #4	$87.56	3.323%	$90.4696	$90.47	$90.45	$90.50
Purchase #5	$125.63	11.270%	$139.7885	$139.79	$139.80	$139.80
Purchase #6	$93.84	3.190%	$96.8335	$96.83	$96.85	$96.80
Purchase #7	$122.80	11.237%	$136.599	$136.60	$136.60	$136.60
7 purchase totals =	$808.65		$873.5604	$873.56	$873.55	$873.50