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	$12.53	9.242%	$13.688	$13.69	$13.70	$13.70
Purchase #2	$249.29	8.449%	$270.3525	$270.35	$270.35	$270.40
Purchase #3	$54.58	8.394%	$59.1614	$59.16	$59.15	$59.20
Purchase #4	$83.51	8.108%	$90.281	$90.28	$90.30	$90.30
Purchase #5	$136.31	6.379%	$145.0052	$145.01	$145.00	$145.00
Purchase #6	$227.82	12.481%	$256.2542	$256.25	$256.25	$256.30
Purchase #7	$129.72	6.183%	$137.7406	$137.74	$137.75	$137.70
7 purchase totals =	$893.76		$972.4829	$972.48	$972.50	$972.60