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	$166.66	7.856%	$179.7528	$179.75	$179.75	$179.80
Purchase #2	$215.89	10.775%	$239.1521	$239.15	$239.15	$239.20
Purchase #3	$144.34	11.218%	$160.5321	$160.53	$160.55	$160.50
Purchase #4	$129.31	9.128%	$141.1134	$141.11	$141.10	$141.10
Purchase #5	$37.50	9.599%	$41.0996	$41.10	$41.10	$41.10
Purchase #6	$82.62	7.806%	$89.0693	$89.07	$89.05	$89.10
Purchase #7	$146.76	12.197%	$164.6603	$164.66	$164.65	$164.70
7 purchase totals =	$923.08		$1,015.3796	$1,015.37	$1,015.35	$1,015.50