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	$151.48	9.175%	$165.3783	$165.38	$165.40	$165.40
Purchase #2	$176.63	6.313%	$187.7807	$187.78	$187.80	$187.80
Purchase #3	$169.85	10.537%	$187.7471	$187.75	$187.75	$187.70
Purchase #4	$40.78	11.144%	$45.3245	$45.32	$45.30	$45.30
Purchase #5	$83.71	3.245%	$86.4264	$86.43	$86.45	$86.40
Purchase #6	$33.81	10.643%	$37.4084	$37.41	$37.40	$37.40
Purchase #7	$109.38	11.499%	$121.9576	$121.96	$121.95	$122.00
7 purchase totals =	$765.64		$832.0230	$832.03	$832.05	$832.00