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	$57.37	4.224%	$59.7933	$59.79	$59.80	$59.80
Purchase #2	$84.71	5.261%	$89.1666	$89.17	$89.15	$89.20
Purchase #3	$227.25	9.703%	$249.3001	$249.30	$249.30	$249.30
Purchase #4	$196.37	8.525%	$213.1105	$213.11	$213.10	$213.10
Purchase #5	$164.51	11.145%	$182.8446	$182.84	$182.85	$182.80
Purchase #6	$234.52	12.491%	$263.8139	$263.81	$263.80	$263.80
Purchase #7	$20.72	9.572%	$22.7033	$22.70	$22.70	$22.70
7 purchase totals =	$985.45		$1,080.7323	$1,080.72	$1,080.70	$1,080.70