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	$96.53	13.261%	$109.3308	$109.33	$109.35	$109.30
Purchase #2	$227.64	6.524%	$242.4912	$242.49	$242.50	$242.50
Purchase #3	$233.75	11.367%	$260.3204	$260.32	$260.30	$260.30
Purchase #4	$186.55	10.166%	$205.5147	$205.51	$205.50	$205.50
Purchase #5	$68.50	5.442%	$72.2278	$72.23	$72.25	$72.20
Purchase #6	$90.81	5.578%	$95.8754	$95.88	$95.90	$95.90
Purchase #7	$133.59	7.671%	$143.8377	$143.84	$143.85	$143.80
7 purchase totals =	$1,037.37		$1,129.5980	$1,129.60	$1,129.65	$1,129.50