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	$189.74	13.806%	$215.9355	$215.94	$215.95	$215.90
Purchase #2	$93.39	6.429%	$99.394	$99.39	$99.40	$99.40
Purchase #3	$22.61	12.737%	$25.4898	$25.49	$25.50	$25.50
Purchase #4	$115.58	6.755%	$123.3874	$123.39	$123.40	$123.40
Purchase #5	$34.70	12.395%	$39.0011	$39.00	$39.00	$39.00
Purchase #6	$238.89	6.262%	$253.8493	$253.85	$253.85	$253.80
Purchase #7	$42.88	10.866%	$47.5393	$47.54	$47.55	$47.50
7 purchase totals =	$737.79		$804.5964	$804.60	$804.65	$804.50