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	$84.52	7.543%	$90.8953	$90.90	$90.90	$90.90
Purchase #2	$73.88	12.541%	$83.1453	$83.15	$83.15	$83.10
Purchase #3	$85.96	10.388%	$94.8895	$94.89	$94.90	$94.90
Purchase #4	$186.38	9.271%	$203.6593	$203.66	$203.65	$203.70
Purchase #5	$211.74	12.643%	$238.5103	$238.51	$238.50	$238.50
Purchase #6	$68.43	11.648%	$76.4007	$76.40	$76.40	$76.40
Purchase #7	$132.28	6.633%	$141.0541	$141.05	$141.05	$141.10
7 purchase totals =	$843.19		$928.5545	$928.56	$928.55	$928.60