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	$22.73	12.675%	$25.611	$25.61	$25.60	$25.60
Purchase #2	$198.94	11.753%	$222.3214	$222.32	$222.30	$222.30
Purchase #3	$166.89	12.824%	$188.292	$188.29	$188.30	$188.30
Purchase #4	$226.40	3.183%	$233.6063	$233.61	$233.60	$233.60
Purchase #5	$46.30	7.553%	$49.797	$49.80	$49.80	$49.80
Purchase #6	$77.88	9.373%	$85.1797	$85.18	$85.20	$85.20
Purchase #7	$155.62	4.173%	$162.114	$162.11	$162.10	$162.10
7 purchase totals =	$894.76		$966.9214	$966.92	$966.90	$966.90