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	$49.91	8.214%	$54.0096	$54.01	$54.00	$54.00
Purchase #2	$90.58	11.869%	$101.3309	$101.33	$101.35	$101.30
Purchase #3	$119.88	9.577%	$131.3609	$131.36	$131.35	$131.40
Purchase #4	$166.53	12.828%	$187.8925	$187.89	$187.90	$187.90
Purchase #5	$156.72	13.175%	$177.3679	$177.37	$177.35	$177.40
Purchase #6	$244.40	9.215%	$266.9215	$266.92	$266.90	$266.90
Purchase #7	$55.44	3.692%	$57.4868	$57.49	$57.50	$57.50
7 purchase totals =	$883.46		$976.3701	$976.37	$976.35	$976.40