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	$124.89	11.309%	$139.0138	$139.01	$139.00	$139.00
Purchase #2	$175.84	5.518%	$185.5429	$185.54	$185.55	$185.50
Purchase #3	$179.25	6.576%	$191.0375	$191.04	$191.05	$191.00
Purchase #4	$57.60	8.619%	$62.5645	$62.56	$62.55	$62.60
Purchase #5	$250.92	6.592%	$267.4606	$267.46	$267.45	$267.50
Purchase #6	$7.27	13.603%	$8.2589	$8.26	$8.25	$8.30
Purchase #7	$51.83	6.332%	$55.1119	$55.11	$55.10	$55.10
7 purchase totals =	$847.60		$908.9901	$908.98	$908.95	$909.00