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	$113.85	9.283%	$124.4187	$124.42	$124.40	$124.40
Purchase #2	$97.39	5.819%	$103.0571	$103.06	$103.05	$103.10
Purchase #3	$89.32	6.827%	$95.4179	$95.42	$95.40	$95.40
Purchase #4	$49.57	13.403%	$56.2139	$56.21	$56.20	$56.20
Purchase #5	$6.99	11.347%	$7.7832	$7.78	$7.80	$7.80
Purchase #6	$49.29	3.116%	$50.8259	$50.83	$50.85	$50.80
Purchase #7	$84.55	11.547%	$94.313	$94.31	$94.30	$94.30
7 purchase totals =	$490.96		$532.0297	$532.03	$532.00	$532.00