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	$40.99	4.566%	$42.8616	$42.86	$42.85	$42.90
Purchase #2	$133.74	8.535%	$145.1547	$145.15	$145.15	$145.20
Purchase #3	$112.72	3.328%	$116.4713	$116.47	$116.45	$116.50
Purchase #4	$101.88	7.199%	$109.2143	$109.21	$109.20	$109.20
Purchase #5	$78.25	13.688%	$88.9609	$88.96	$88.95	$89.00
Purchase #6	$140.41	3.531%	$145.3679	$145.37	$145.35	$145.40
Purchase #7	$169.33	7.861%	$182.641	$182.64	$182.65	$182.60
7 purchase totals =	$777.32		$830.6717	$830.66	$830.60	$830.80