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	$242.61	6.506%	$258.3942	$258.39	$258.40	$258.40
Purchase #2	$75.78	3.609%	$78.5149	$78.51	$78.50	$78.50
Purchase #3	$158.43	7.659%	$170.5642	$170.56	$170.55	$170.60
Purchase #4	$231.67	5.735%	$244.9563	$244.96	$244.95	$245.00
Purchase #5	$197.85	6.577%	$210.8626	$210.86	$210.85	$210.90
Purchase #6	$171.39	12.309%	$192.4864	$192.49	$192.50	$192.50
Purchase #7	$233.37	3.317%	$241.1109	$241.11	$241.10	$241.10
7 purchase totals =	$1,311.10		$1,396.8895	$1,396.88	$1,396.85	$1,397.00