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	$52.78	8.596%	$57.317	$57.32	$57.30	$57.30
Purchase #2	$30.87	5.483%	$32.5626	$32.56	$32.55	$32.60
Purchase #3	$108.58	11.811%	$121.4044	$121.40	$121.40	$121.40
Purchase #4	$118.78	10.750%	$131.5489	$131.55	$131.55	$131.50
Purchase #5	$35.88	3.730%	$37.2183	$37.22	$37.20	$37.20
Purchase #6	$5.66	7.505%	$6.0848	$6.08	$6.10	$6.10
Purchase #7	$31.35	6.755%	$33.4677	$33.47	$33.45	$33.50
7 purchase totals =	$383.90		$419.6037	$419.60	$419.55	$419.60