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	$105.83	8.455%	$114.7779	$114.78	$114.80	$114.80
Purchase #2	$158.48	4.374%	$165.4119	$165.41	$165.40	$165.40
Purchase #3	$76.36	13.405%	$86.5961	$86.60	$86.60	$86.60
Purchase #4	$116.82	7.746%	$125.8689	$125.87	$125.85	$125.90
Purchase #5	$90.59	13.450%	$102.7744	$102.77	$102.75	$102.80
Purchase #6	$66.33	8.568%	$72.0132	$72.01	$72.00	$72.00
Purchase #7	$190.61	10.874%	$211.3369	$211.34	$211.35	$211.30
7 purchase totals =	$805.02		$878.7793	$878.78	$878.75	$878.80