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	$45.35	12.171%	$50.8695	$50.87	$50.85	$50.90
Purchase #2	$91.77	9.589%	$100.5698	$100.57	$100.55	$100.60
Purchase #3	$95.45	10.330%	$105.31	$105.31	$105.30	$105.30
Purchase #4	$177.35	12.291%	$199.1481	$199.15	$199.15	$199.10
Purchase #5	$226.59	3.694%	$234.9602	$234.96	$234.95	$235.00
Purchase #6	$214.86	13.300%	$243.4364	$243.44	$243.45	$243.40
Purchase #7	$47.63	9.139%	$51.9829	$51.98	$52.00	$52.00
7 purchase totals =	$899.00		$986.2769	$986.28	$986.25	$986.30