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	$51.32	12.134%	$57.5472	$57.55	$57.55	$57.50
Purchase #2	$241.92	11.397%	$269.4916	$269.49	$269.50	$269.50
Purchase #3	$86.84	11.579%	$96.8952	$96.90	$96.90	$96.90
Purchase #4	$32.48	13.602%	$36.8979	$36.90	$36.90	$36.90
Purchase #5	$40.66	4.607%	$42.5332	$42.53	$42.55	$42.50
Purchase #6	$205.28	7.533%	$220.7437	$220.74	$220.75	$220.70
Purchase #7	$75.78	6.760%	$80.9027	$80.90	$80.90	$80.90
7 purchase totals =	$734.28		$805.0115	$805.01	$805.05	$804.90