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	$46.36	11.552%	$51.7155	$51.72	$51.70	$51.70
Purchase #2	$56.78	5.236%	$59.753	$59.75	$59.75	$59.80
Purchase #3	$219.32	13.294%	$248.4764	$248.48	$248.50	$248.50
Purchase #4	$135.66	6.449%	$144.4087	$144.41	$144.40	$144.40
Purchase #5	$36.39	13.176%	$41.1847	$41.18	$41.20	$41.20
Purchase #6	$163.90	11.410%	$182.601	$182.60	$182.60	$182.60
Purchase #7	$147.32	6.388%	$156.7308	$156.73	$156.75	$156.70
7 purchase totals =	$805.73		$884.8701	$884.87	$884.90	$884.90