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	$79.97	4.437%	$83.5183	$83.52	$83.50	$83.50
Purchase #2	$65.86	11.415%	$73.3779	$73.38	$73.40	$73.40
Purchase #3	$131.59	4.157%	$137.0602	$137.06	$137.05	$137.10
Purchase #4	$137.81	8.729%	$149.8394	$149.84	$149.85	$149.80
Purchase #5	$87.92	4.476%	$91.8553	$91.86	$91.85	$91.90
Purchase #6	$93.90	6.270%	$99.7875	$99.79	$99.80	$99.80
Purchase #7	$237.60	10.448%	$262.4244	$262.42	$262.40	$262.40
7 purchase totals =	$834.65		$897.8630	$897.87	$897.85	$897.90