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	$79.98	12.531%	$90.0023	$90.00	$90.00	$90.00
Purchase #2	$103.75	12.309%	$116.5206	$116.52	$116.50	$116.50
Purchase #3	$41.57	10.467%	$45.9211	$45.92	$45.90	$45.90
Purchase #4	$7.51	5.700%	$7.9381	$7.94	$7.95	$7.90
Purchase #5	$204.36	9.241%	$223.2449	$223.24	$223.25	$223.20
Purchase #6	$228.43	10.774%	$253.041	$253.04	$253.05	$253.00
Purchase #7	$41.95	10.674%	$46.4277	$46.43	$46.45	$46.40
7 purchase totals =	$707.55		$783.0957	$783.09	$783.10	$782.90