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	$220.35	12.245%	$247.3319	$247.33	$247.35	$247.30
Purchase #2	$36.68	3.323%	$37.8989	$37.90	$37.90	$37.90
Purchase #3	$203.69	7.445%	$218.8547	$218.85	$218.85	$218.90
Purchase #4	$19.82	7.322%	$21.2712	$21.27	$21.25	$21.30
Purchase #5	$175.66	8.670%	$190.8897	$190.89	$190.90	$190.90
Purchase #6	$5.96	10.730%	$6.5995	$6.60	$6.60	$6.60
Purchase #7	$197.85	7.821%	$213.3238	$213.32	$213.30	$213.30
7 purchase totals =	$860.01		$936.1697	$936.16	$936.15	$936.20