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	$26.59	6.180%	$28.2333	$28.23	$28.25	$28.20
Purchase #2	$14.76	6.726%	$15.7528	$15.75	$15.75	$15.80
Purchase #3	$183.68	11.776%	$205.3102	$205.31	$205.30	$205.30
Purchase #4	$93.78	5.802%	$99.2211	$99.22	$99.20	$99.20
Purchase #5	$56.34	7.774%	$60.7199	$60.72	$60.70	$60.70
Purchase #6	$81.58	11.462%	$90.9307	$90.93	$90.95	$90.90
Purchase #7	$83.66	9.745%	$91.8127	$91.81	$91.80	$91.80
7 purchase totals =	$540.39		$591.9807	$591.97	$591.95	$591.90