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	$46.78	4.500%	$48.8851	$48.89	$48.90	$48.90
Purchase #2	$185.51	13.802%	$211.1141	$211.11	$211.10	$211.10
Purchase #3	$169.39	6.132%	$179.777	$179.78	$179.80	$179.80
Purchase #4	$160.55	5.846%	$169.9358	$169.94	$169.95	$169.90
Purchase #5	$89.34	12.285%	$100.3154	$100.32	$100.30	$100.30
Purchase #6	$205.94	9.625%	$225.7617	$225.76	$225.75	$225.80
Purchase #7	$95.30	13.647%	$108.3056	$108.31	$108.30	$108.30
7 purchase totals =	$952.81		$1,044.0947	$1,044.11	$1,044.10	$1,044.10