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	$28.78	12.618%	$32.4115	$32.41	$32.40	$32.40
Purchase #2	$168.84	13.823%	$192.1788	$192.18	$192.20	$192.20
Purchase #3	$241.38	6.817%	$257.8349	$257.83	$257.85	$257.80
Purchase #4	$237.80	7.394%	$255.3829	$255.38	$255.40	$255.40
Purchase #5	$71.51	9.370%	$78.2105	$78.21	$78.20	$78.20
Purchase #6	$118.96	5.301%	$125.2661	$125.27	$125.25	$125.30
Purchase #7	$151.68	5.498%	$160.0194	$160.02	$160.00	$160.00
7 purchase totals =	$1,018.95		$1,101.3041	$1,101.30	$1,101.30	$1,101.30