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	$54.77	8.529%	$59.4413	$59.44	$59.45	$59.40
Purchase #2	$137.96	3.582%	$142.9017	$142.90	$142.90	$142.90
Purchase #3	$226.89	6.426%	$241.47	$241.47	$241.45	$241.50
Purchase #4	$196.41	5.758%	$207.7193	$207.72	$207.70	$207.70
Purchase #5	$85.53	7.376%	$91.8387	$91.84	$91.85	$91.80
Purchase #6	$60.62	4.823%	$63.5437	$63.54	$63.55	$63.50
Purchase #7	$64.97	4.511%	$67.9008	$67.90	$67.90	$67.90
7 purchase totals =	$827.15		$874.8155	$874.81	$874.80	$874.70