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	$249.93	7.558%	$268.8197	$268.82	$268.80	$268.80
Purchase #2	$99.47	4.213%	$103.6607	$103.66	$103.65	$103.70
Purchase #3	$67.96	5.131%	$71.447	$71.45	$71.45	$71.40
Purchase #4	$86.89	4.663%	$90.9417	$90.94	$90.95	$90.90
Purchase #5	$66.61	4.290%	$69.4676	$69.47	$69.45	$69.50
Purchase #6	$135.47	10.165%	$149.2405	$149.24	$149.25	$149.20
Purchase #7	$87.95	7.561%	$94.5999	$94.60	$94.60	$94.60
7 purchase totals =	$794.28		$848.1771	$848.18	$848.15	$848.10