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	$220.49	13.611%	$250.5009	$250.50	$250.50	$250.50
Purchase #2	$39.26	4.267%	$40.9352	$40.94	$40.95	$40.90
Purchase #3	$79.93	3.666%	$82.8602	$82.86	$82.85	$82.90
Purchase #4	$159.61	12.828%	$180.0848	$180.08	$180.10	$180.10
Purchase #5	$119.40	5.779%	$126.3001	$126.30	$126.30	$126.30
Purchase #6	$28.59	11.489%	$31.8747	$31.87	$31.85	$31.90
Purchase #7	$223.69	12.461%	$251.564	$251.56	$251.55	$251.60
7 purchase totals =	$870.97		$964.1199	$964.11	$964.10	$964.20