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	$29.60	7.765%	$31.8984	$31.90	$31.90	$31.90
Purchase #2	$32.33	9.874%	$35.5223	$35.52	$35.50	$35.50
Purchase #3	$129.37	13.333%	$146.6189	$146.62	$146.60	$146.60
Purchase #4	$177.40	5.628%	$187.3841	$187.38	$187.40	$187.40
Purchase #5	$82.39	11.693%	$92.0239	$92.02	$92.00	$92.00
Purchase #6	$57.89	9.848%	$63.591	$63.59	$63.60	$63.60
Purchase #7	$234.39	6.325%	$249.2152	$249.22	$249.20	$249.20
7 purchase totals =	$743.37		$806.2538	$806.25	$806.20	$806.20