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	$40.25	10.349%	$44.4155	$44.42	$44.40	$44.40
Purchase #2	$32.36	3.612%	$33.5288	$33.53	$33.55	$33.50
Purchase #3	$45.55	9.139%	$49.7128	$49.71	$49.70	$49.70
Purchase #4	$164.61	4.201%	$171.5253	$171.53	$171.55	$171.50
Purchase #5	$6.80	6.482%	$7.2408	$7.24	$7.25	$7.20
Purchase #6	$91.53	12.836%	$103.2788	$103.28	$103.30	$103.30
Purchase #7	$218.93	13.684%	$248.8884	$248.89	$248.90	$248.90
7 purchase totals =	$600.03		$658.5904	$658.60	$658.65	$658.50