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	$54.74	4.745%	$57.3374	$57.34	$57.35	$57.30
Purchase #2	$135.41	6.820%	$144.645	$144.65	$144.65	$144.60
Purchase #3	$60.46	4.319%	$63.0713	$63.07	$63.05	$63.10
Purchase #4	$123.97	12.489%	$139.4526	$139.45	$139.45	$139.50
Purchase #5	$56.86	4.267%	$59.2862	$59.29	$59.30	$59.30
Purchase #6	$189.48	12.335%	$212.8524	$212.85	$212.85	$212.90
Purchase #7	$9.61	7.180%	$10.3	$10.30	$10.30	$10.30
7 purchase totals =	$630.53		$686.9449	$686.95	$686.95	$687.00