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	$124.58	12.262%	$139.856	$139.86	$139.85	$139.90
Purchase #2	$67.71	7.688%	$72.9155	$72.92	$72.90	$72.90
Purchase #3	$237.36	7.319%	$254.7324	$254.73	$254.75	$254.70
Purchase #4	$97.51	9.583%	$106.8544	$106.85	$106.85	$106.90
Purchase #5	$249.85	5.550%	$263.7167	$263.72	$263.70	$263.70
Purchase #6	$37.96	3.739%	$39.3793	$39.38	$39.40	$39.40
Purchase #7	$45.80	11.485%	$51.0601	$51.06	$51.05	$51.10
7 purchase totals =	$860.77		$928.5144	$928.52	$928.50	$928.60