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	$239.33	11.327%	$266.4389	$266.44	$266.45	$266.40
Purchase #2	$169.36	8.539%	$183.8217	$183.82	$183.80	$183.80
Purchase #3	$60.69	11.865%	$67.8909	$67.89	$67.90	$67.90
Purchase #4	$188.90	8.194%	$204.3785	$204.38	$204.40	$204.40
Purchase #5	$38.59	12.699%	$43.4905	$43.49	$43.50	$43.50
Purchase #6	$18.81	11.740%	$21.0183	$21.02	$21.00	$21.00
Purchase #7	$85.53	12.577%	$96.2871	$96.29	$96.30	$96.30
7 purchase totals =	$801.21		$883.3259	$883.33	$883.35	$883.30