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	$45.36	8.791%	$49.3476	$49.35	$49.35	$49.30
Purchase #2	$246.37	11.257%	$274.1039	$274.10	$274.10	$274.10
Purchase #3	$75.89	13.413%	$86.0691	$86.07	$86.05	$86.10
Purchase #4	$111.97	11.150%	$124.4547	$124.45	$124.45	$124.50
Purchase #5	$38.61	10.236%	$42.5621	$42.56	$42.55	$42.60
Purchase #6	$214.81	6.168%	$228.0595	$228.06	$228.05	$228.10
Purchase #7	$86.66	9.494%	$94.8875	$94.89	$94.90	$94.90
7 purchase totals =	$819.67		$899.4844	$899.48	$899.45	$899.60