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	$31.84	3.430%	$32.9321	$32.93	$32.95	$32.90
Purchase #2	$91.28	9.693%	$100.1278	$100.13	$100.15	$100.10
Purchase #3	$65.34	8.831%	$71.1102	$71.11	$71.10	$71.10
Purchase #4	$33.60	5.494%	$35.446	$35.45	$35.45	$35.40
Purchase #5	$128.44	6.371%	$136.6229	$136.62	$136.60	$136.60
Purchase #6	$151.55	8.677%	$164.7	$164.70	$164.70	$164.70
Purchase #7	$18.27	11.661%	$20.4005	$20.40	$20.40	$20.40
7 purchase totals =	$520.32		$561.3395	$561.34	$561.35	$561.20