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	$135.72	12.373%	$152.5126	$152.51	$152.50	$152.50
Purchase #2	$146.56	9.814%	$160.9434	$160.94	$160.95	$160.90
Purchase #3	$205.70	9.831%	$225.9224	$225.92	$225.90	$225.90
Purchase #4	$86.51	6.581%	$92.2032	$92.20	$92.20	$92.20
Purchase #5	$27.73	5.489%	$29.2521	$29.25	$29.25	$29.30
Purchase #6	$76.85	10.786%	$85.139	$85.14	$85.15	$85.10
Purchase #7	$104.89	5.203%	$110.3474	$110.35	$110.35	$110.30
7 purchase totals =	$783.96		$856.3201	$856.31	$856.30	$856.20