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	$209.47	6.285%	$222.6352	$222.64	$222.65	$222.60
Purchase #2	$43.98	13.112%	$49.7467	$49.75	$49.75	$49.70
Purchase #3	$99.97	10.484%	$110.4509	$110.45	$110.45	$110.50
Purchase #4	$179.76	4.488%	$187.8276	$187.83	$187.85	$187.80
Purchase #5	$50.72	7.141%	$54.3419	$54.34	$54.35	$54.30
Purchase #6	$244.37	7.760%	$263.3331	$263.33	$263.35	$263.30
Purchase #7	$90.97	10.451%	$100.4773	$100.48	$100.50	$100.50
7 purchase totals =	$919.24		$988.8127	$988.82	$988.90	$988.70