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	$65.67	4.466%	$68.6028	$68.60	$68.60	$68.60
Purchase #2	$82.56	10.826%	$91.4979	$91.50	$91.50	$91.50
Purchase #3	$92.55	12.659%	$104.2659	$104.27	$104.25	$104.30
Purchase #4	$76.63	9.109%	$83.6102	$83.61	$83.60	$83.60
Purchase #5	$25.97	9.637%	$28.4727	$28.47	$28.45	$28.50
Purchase #6	$114.84	10.746%	$127.1807	$127.18	$127.20	$127.20
Purchase #7	$140.38	11.350%	$156.3131	$156.31	$156.30	$156.30
7 purchase totals =	$598.60		$659.9433	$659.94	$659.90	$660.00