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	$50.90	6.352%	$54.1332	$54.13	$54.15	$54.10
Purchase #2	$53.71	7.798%	$57.8983	$57.90	$57.90	$57.90
Purchase #3	$98.70	13.482%	$112.0067	$112.01	$112.00	$112.00
Purchase #4	$32.86	13.746%	$37.3769	$37.38	$37.40	$37.40
Purchase #5	$86.80	6.237%	$92.2137	$92.21	$92.20	$92.20
Purchase #6	$224.37	11.391%	$249.928	$249.93	$249.95	$249.90
Purchase #7	$194.50	10.672%	$215.257	$215.26	$215.25	$215.30
7 purchase totals =	$741.84		$818.8138	$818.82	$818.85	$818.80