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	$93.90	6.481%	$99.9857	$99.99	$100.00	$100.00
Purchase #2	$98.75	9.320%	$107.9535	$107.95	$107.95	$108.00
Purchase #3	$77.32	6.531%	$82.3698	$82.37	$82.35	$82.40
Purchase #4	$121.50	5.451%	$128.123	$128.12	$128.10	$128.10
Purchase #5	$234.85	11.107%	$260.9348	$260.93	$260.95	$260.90
Purchase #6	$218.84	6.690%	$233.4804	$233.48	$233.50	$233.50
Purchase #7	$58.92	11.272%	$65.5615	$65.56	$65.55	$65.60
7 purchase totals =	$904.08		$978.4087	$978.40	$978.40	$978.50