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	$120.71	6.754%	$128.8628	$128.86	$128.85	$128.90
Purchase #2	$112.93	9.296%	$123.428	$123.43	$123.45	$123.40
Purchase #3	$150.52	9.220%	$164.3979	$164.40	$164.40	$164.40
Purchase #4	$130.28	11.235%	$144.917	$144.92	$144.90	$144.90
Purchase #5	$154.43	13.153%	$174.7422	$174.74	$174.75	$174.70
Purchase #6	$168.42	5.709%	$178.0351	$178.04	$178.05	$178.00
Purchase #7	$81.86	5.507%	$86.368	$86.37	$86.35	$86.40
7 purchase totals =	$919.15		$1,000.7510	$1,000.76	$1,000.75	$1,000.70