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	$213.84	12.323%	$240.1915	$240.19	$240.20	$240.20
Purchase #2	$81.76	11.129%	$90.8591	$90.86	$90.85	$90.90
Purchase #3	$150.97	3.430%	$156.1483	$156.15	$156.15	$156.10
Purchase #4	$37.59	8.507%	$40.7878	$40.79	$40.80	$40.80
Purchase #5	$33.68	12.397%	$37.8553	$37.86	$37.85	$37.90
Purchase #6	$171.93	12.433%	$193.3061	$193.31	$193.30	$193.30
Purchase #7	$91.66	9.717%	$100.5666	$100.57	$100.55	$100.60
7 purchase totals =	$781.43		$859.7147	$859.73	$859.70	$859.80