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	$123.56	6.613%	$131.731	$131.73	$131.75	$131.70
Purchase #2	$107.90	13.743%	$122.7287	$122.73	$122.75	$122.70
Purchase #3	$95.50	3.664%	$98.9991	$99.00	$99.00	$99.00
Purchase #4	$132.38	12.490%	$148.9143	$148.91	$148.90	$148.90
Purchase #5	$70.38	11.560%	$78.5159	$78.52	$78.50	$78.50
Purchase #6	$82.80	8.460%	$89.8049	$89.80	$89.80	$89.80
Purchase #7	$243.57	7.774%	$262.5051	$262.51	$262.50	$262.50
7 purchase totals =	$856.09		$933.1990	$933.20	$933.20	$933.10