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	$135.91	8.789%	$147.8551	$147.86	$147.85	$147.90
Purchase #2	$106.60	3.717%	$110.5623	$110.56	$110.55	$110.60
Purchase #3	$78.86	13.194%	$89.2648	$89.26	$89.25	$89.30
Purchase #4	$10.71	11.691%	$11.9621	$11.96	$11.95	$12.00
Purchase #5	$36.43	12.508%	$40.9867	$40.99	$41.00	$41.00
Purchase #6	$210.56	8.241%	$227.9122	$227.91	$227.90	$227.90
Purchase #7	$35.51	11.280%	$39.5155	$39.52	$39.50	$39.50
7 purchase totals =	$614.58		$668.0587	$668.06	$668.00	$668.20