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	$97.92	5.190%	$103.002	$103.00	$103.00	$103.00
Purchase #2	$152.31	5.428%	$160.5774	$160.58	$160.60	$160.60
Purchase #3	$86.32	5.231%	$90.8354	$90.84	$90.85	$90.80
Purchase #4	$160.99	9.166%	$175.7463	$175.75	$175.75	$175.70
Purchase #5	$174.94	7.314%	$187.7351	$187.74	$187.75	$187.70
Purchase #6	$41.68	6.659%	$44.4555	$44.46	$44.45	$44.50
Purchase #7	$52.35	10.360%	$57.7735	$57.77	$57.75	$57.80
7 purchase totals =	$766.51		$820.1252	$820.14	$820.15	$820.10