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	$247.88	3.310%	$256.0848	$256.08	$256.10	$256.10
Purchase #2	$206.37	8.288%	$223.4739	$223.47	$223.45	$223.50
Purchase #3	$151.60	8.786%	$164.9196	$164.92	$164.90	$164.90
Purchase #4	$47.83	13.539%	$54.3057	$54.31	$54.30	$54.30
Purchase #5	$52.98	5.465%	$55.8754	$55.88	$55.90	$55.90
Purchase #6	$154.33	7.664%	$166.1579	$166.16	$166.15	$166.20
Purchase #7	$35.27	5.246%	$37.1203	$37.12	$37.10	$37.10
7 purchase totals =	$896.26		$957.9376	$957.94	$957.90	$958.00