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	$250.81	12.460%	$282.0609	$282.06	$282.05	$282.10
Purchase #2	$92.77	8.432%	$100.5924	$100.59	$100.60	$100.60
Purchase #3	$33.71	12.500%	$37.9238	$37.92	$37.90	$37.90
Purchase #4	$128.62	12.708%	$144.965	$144.97	$144.95	$145.00
Purchase #5	$147.59	8.120%	$159.5743	$159.57	$159.55	$159.60
Purchase #6	$38.40	8.424%	$41.6348	$41.63	$41.65	$41.60
Purchase #7	$51.70	8.638%	$56.1658	$56.17	$56.15	$56.20
7 purchase totals =	$743.60		$822.9170	$822.91	$822.85	$823.00