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	$31.81	3.428%	$32.9004	$32.90	$32.90	$32.90
Purchase #2	$60.44	7.334%	$64.8727	$64.87	$64.85	$64.90
Purchase #3	$85.40	3.777%	$88.6256	$88.63	$88.65	$88.60
Purchase #4	$138.87	13.409%	$157.4911	$157.49	$157.50	$157.50
Purchase #5	$86.63	4.268%	$90.3274	$90.33	$90.35	$90.30
Purchase #6	$59.96	7.548%	$64.4858	$64.49	$64.50	$64.50
Purchase #7	$42.70	4.378%	$44.5694	$44.57	$44.55	$44.60
7 purchase totals =	$505.81		$543.2724	$543.28	$543.30	$543.30