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	$56.64	4.713%	$59.3094	$59.31	$59.30	$59.30
Purchase #2	$138.92	5.480%	$146.5328	$146.53	$146.55	$146.50
Purchase #3	$88.66	13.292%	$100.4447	$100.44	$100.45	$100.40
Purchase #4	$79.82	7.377%	$85.7083	$85.71	$85.70	$85.70
Purchase #5	$161.85	4.350%	$168.8905	$168.89	$168.90	$168.90
Purchase #6	$189.25	11.780%	$211.5437	$211.54	$211.55	$211.50
Purchase #7	$187.81	6.570%	$200.1491	$200.15	$200.15	$200.10
7 purchase totals =	$902.95		$972.5785	$972.57	$972.60	$972.40