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	$204.28	10.134%	$224.9817	$224.98	$225.00	$225.00
Purchase #2	$104.49	4.817%	$109.5233	$109.52	$109.50	$109.50
Purchase #3	$82.59	11.575%	$92.1498	$92.15	$92.15	$92.10
Purchase #4	$71.38	7.311%	$76.5986	$76.60	$76.60	$76.60
Purchase #5	$92.89	11.642%	$103.7043	$103.70	$103.70	$103.70
Purchase #6	$63.56	12.260%	$71.3525	$71.35	$71.35	$71.40
Purchase #7	$200.31	11.169%	$222.6826	$222.68	$222.70	$222.70
7 purchase totals =	$819.50		$900.9928	$900.98	$901.00	$901.00