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	$100.33	12.776%	$113.1482	$113.15	$113.15	$113.10
Purchase #2	$85.88	11.511%	$95.7656	$95.77	$95.75	$95.80
Purchase #3	$225.32	7.222%	$241.5926	$241.59	$241.60	$241.60
Purchase #4	$183.87	4.102%	$191.4123	$191.41	$191.40	$191.40
Purchase #5	$29.42	5.520%	$31.044	$31.04	$31.05	$31.00
Purchase #6	$224.50	11.761%	$250.9034	$250.90	$250.90	$250.90
Purchase #7	$54.37	10.543%	$60.1022	$60.10	$60.10	$60.10
7 purchase totals =	$903.69		$983.9683	$983.96	$983.95	$983.90