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	$12.61	9.546%	$13.8138	$13.81	$13.80	$13.80
Purchase #2	$37.36	12.335%	$41.9684	$41.97	$41.95	$42.00
Purchase #3	$35.59	9.477%	$38.9629	$38.96	$38.95	$39.00
Purchase #4	$32.94	12.872%	$37.18	$37.18	$37.20	$37.20
Purchase #5	$89.34	5.550%	$94.2984	$94.30	$94.30	$94.30
Purchase #6	$135.32	10.544%	$149.5881	$149.59	$149.60	$149.60
Purchase #7	$39.60	7.354%	$42.5122	$42.51	$42.50	$42.50
7 purchase totals =	$382.76		$418.3238	$418.32	$418.30	$418.40