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	$217.43	12.760%	$245.1741	$245.17	$245.15	$245.20
Purchase #2	$224.75	9.369%	$245.8068	$245.81	$245.80	$245.80
Purchase #3	$91.34	9.844%	$100.3315	$100.33	$100.35	$100.30
Purchase #4	$74.36	10.466%	$82.1425	$82.14	$82.15	$82.10
Purchase #5	$249.28	12.740%	$281.0383	$281.04	$281.05	$281.00
Purchase #6	$34.88	3.143%	$35.9763	$35.98	$36.00	$36.00
Purchase #7	$22.88	7.475%	$24.5903	$24.59	$24.60	$24.60
7 purchase totals =	$914.92		$1,015.0598	$1,015.06	$1,015.10	$1,015.00