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	$247.62	12.231%	$277.9064	$277.91	$277.90	$277.90
Purchase #2	$147.76	9.168%	$161.3066	$161.31	$161.30	$161.30
Purchase #3	$225.88	13.762%	$256.9656	$256.97	$256.95	$257.00
Purchase #4	$100.39	3.238%	$103.6406	$103.64	$103.65	$103.60
Purchase #5	$33.52	8.624%	$36.4108	$36.41	$36.40	$36.40
Purchase #6	$29.53	11.560%	$32.9437	$32.94	$32.95	$32.90
Purchase #7	$129.47	9.166%	$141.3372	$141.34	$141.35	$141.30
7 purchase totals =	$914.17		$1,010.5109	$1,010.52	$1,010.50	$1,010.40