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	$26.63	6.118%	$28.2592	$28.26	$28.25	$28.30
Purchase #2	$39.97	8.738%	$43.4626	$43.46	$43.45	$43.50
Purchase #3	$145.59	8.613%	$158.1297	$158.13	$158.15	$158.10
Purchase #4	$166.54	4.763%	$174.4723	$174.47	$174.45	$174.50
Purchase #5	$206.91	13.490%	$234.8222	$234.82	$234.80	$234.80
Purchase #6	$182.51	6.748%	$194.8258	$194.83	$194.85	$194.80
Purchase #7	$206.36	8.493%	$223.8862	$223.89	$223.90	$223.90
7 purchase totals =	$974.51		$1,057.8580	$1,057.86	$1,057.85	$1,057.90