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	$63.74	13.756%	$72.5081	$72.51	$72.50	$72.50
Purchase #2	$198.40	8.332%	$214.9307	$214.93	$214.95	$214.90
Purchase #3	$32.93	7.784%	$35.4933	$35.49	$35.50	$35.50
Purchase #4	$132.53	7.449%	$142.4022	$142.40	$142.40	$142.40
Purchase #5	$33.99	11.527%	$37.908	$37.91	$37.90	$37.90
Purchase #6	$120.82	11.167%	$134.312	$134.31	$134.30	$134.30
Purchase #7	$208.36	6.204%	$221.2867	$221.29	$221.30	$221.30
7 purchase totals =	$790.77		$858.8410	$858.84	$858.85	$858.80