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	$131.78	11.772%	$147.2931	$147.29	$147.30	$147.30
Purchase #2	$151.83	11.619%	$169.4711	$169.47	$169.45	$169.50
Purchase #3	$92.51	10.299%	$102.0376	$102.04	$102.05	$102.00
Purchase #4	$42.74	8.628%	$46.4276	$46.43	$46.45	$46.40
Purchase #5	$83.37	7.585%	$89.6936	$89.69	$89.70	$89.70
Purchase #6	$68.58	5.691%	$72.4829	$72.48	$72.50	$72.50
Purchase #7	$218.72	4.841%	$229.3082	$229.31	$229.30	$229.30
7 purchase totals =	$789.53		$856.7141	$856.71	$856.75	$856.70