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	$37.75	7.333%	$40.5182	$40.52	$40.50	$40.50
Purchase #2	$50.91	11.729%	$56.8812	$56.88	$56.90	$56.90
Purchase #3	$82.59	13.766%	$93.9593	$93.96	$93.95	$94.00
Purchase #4	$30.37	9.216%	$33.1689	$33.17	$33.15	$33.20
Purchase #5	$247.69	9.766%	$271.8794	$271.88	$271.90	$271.90
Purchase #6	$240.35	10.826%	$266.3703	$266.37	$266.35	$266.40
Purchase #7	$163.39	13.604%	$185.6176	$185.62	$185.60	$185.60
7 purchase totals =	$853.05		$948.3949	$948.40	$948.35	$948.50