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	$41.43	13.296%	$46.9385	$46.94	$46.95	$46.90
Purchase #2	$30.72	5.171%	$32.3085	$32.31	$32.30	$32.30
Purchase #3	$17.42	5.231%	$18.3312	$18.33	$18.35	$18.30
Purchase #4	$168.54	7.691%	$181.5024	$181.50	$181.50	$181.50
Purchase #5	$82.34	8.804%	$89.5892	$89.59	$89.60	$89.60
Purchase #6	$124.54	4.745%	$130.4494	$130.45	$130.45	$130.40
Purchase #7	$165.67	3.115%	$170.8306	$170.83	$170.85	$170.80
7 purchase totals =	$630.66		$669.9498	$669.95	$670.00	$669.80