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	$49.49	5.242%	$52.0843	$52.08	$52.10	$52.10
Purchase #2	$234.75	9.550%	$257.1686	$257.17	$257.15	$257.20
Purchase #3	$131.38	5.460%	$138.5533	$138.55	$138.55	$138.60
Purchase #4	$95.34	5.244%	$100.3396	$100.34	$100.35	$100.30
Purchase #5	$115.76	8.769%	$125.911	$125.91	$125.90	$125.90
Purchase #6	$80.76	12.541%	$90.8881	$90.89	$90.90	$90.90
Purchase #7	$234.72	3.544%	$243.0385	$243.04	$243.05	$243.00
7 purchase totals =	$942.20		$1,007.9834	$1,007.98	$1,008.00	$1,008.00