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	$154.44	9.807%	$169.5859	$169.59	$169.60	$169.60
Purchase #2	$175.95	11.775%	$196.6681	$196.67	$196.65	$196.70
Purchase #3	$31.77	4.622%	$33.2384	$33.24	$33.25	$33.20
Purchase #4	$19.65	7.411%	$21.1063	$21.11	$21.10	$21.10
Purchase #5	$12.59	9.779%	$13.8212	$13.82	$13.80	$13.80
Purchase #6	$77.92	9.749%	$85.5164	$85.52	$85.50	$85.50
Purchase #7	$234.57	6.868%	$250.6803	$250.68	$250.70	$250.70
7 purchase totals =	$706.89		$770.6166	$770.63	$770.60	$770.60