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	$37.33	13.851%	$42.5006	$42.50	$42.50	$42.50
Purchase #2	$98.31	10.454%	$108.5873	$108.59	$108.60	$108.60
Purchase #3	$125.78	10.177%	$138.5806	$138.58	$138.60	$138.60
Purchase #4	$186.75	4.382%	$194.9334	$194.93	$194.95	$194.90
Purchase #5	$210.85	10.646%	$233.2971	$233.30	$233.30	$233.30
Purchase #6	$93.43	11.860%	$104.5108	$104.51	$104.50	$104.50
Purchase #7	$120.25	9.250%	$131.3731	$131.37	$131.35	$131.40
7 purchase totals =	$872.70		$953.7829	$953.78	$953.80	$953.80