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	$6.70	4.606%	$7.0086	$7.01	$7.00	$7.00
Purchase #2	$87.59	12.848%	$98.8436	$98.84	$98.85	$98.80
Purchase #3	$242.72	6.604%	$258.7492	$258.75	$258.75	$258.70
Purchase #4	$57.91	6.192%	$61.4958	$61.50	$61.50	$61.50
Purchase #5	$101.42	11.314%	$112.8947	$112.89	$112.90	$112.90
Purchase #6	$184.28	6.655%	$196.5438	$196.54	$196.55	$196.50
Purchase #7	$205.29	8.650%	$223.0476	$223.05	$223.05	$223.00
7 purchase totals =	$885.91		$958.5833	$958.58	$958.60	$958.40