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	$48.27	13.296%	$54.688	$54.69	$54.70	$54.70
Purchase #2	$54.31	3.266%	$56.0838	$56.08	$56.10	$56.10
Purchase #3	$88.82	4.477%	$92.7965	$92.80	$92.80	$92.80
Purchase #4	$94.41	10.732%	$104.5421	$104.54	$104.55	$104.50
Purchase #5	$18.65	12.258%	$20.9361	$20.94	$20.95	$20.90
Purchase #6	$41.51	9.273%	$45.3592	$45.36	$45.35	$45.40
Purchase #7	$42.78	10.348%	$47.2069	$47.21	$47.20	$47.20
7 purchase totals =	$388.75		$421.6126	$421.62	$421.65	$421.60