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	$168.95	11.851%	$188.9723	$188.97	$188.95	$189.00
Purchase #2	$6.89	8.364%	$7.4663	$7.47	$7.45	$7.50
Purchase #3	$136.82	5.112%	$143.8142	$143.81	$143.80	$143.80
Purchase #4	$72.76	3.827%	$75.5445	$75.54	$75.55	$75.50
Purchase #5	$41.56	9.325%	$45.4355	$45.44	$45.45	$45.40
Purchase #6	$157.59	8.219%	$170.5423	$170.54	$170.55	$170.50
Purchase #7	$7.35	7.872%	$7.9286	$7.93	$7.95	$7.90
7 purchase totals =	$591.92		$639.7037	$639.70	$639.70	$639.60