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	$29.79	13.738%	$33.8826	$33.88	$33.90	$33.90
Purchase #2	$80.46	13.201%	$91.0815	$91.08	$91.10	$91.10
Purchase #3	$112.89	9.215%	$123.2928	$123.29	$123.30	$123.30
Purchase #4	$52.64	4.297%	$54.9019	$54.90	$54.90	$54.90
Purchase #5	$80.59	11.229%	$89.6395	$89.64	$89.65	$89.60
Purchase #6	$176.40	12.525%	$198.4941	$198.49	$198.50	$198.50
Purchase #7	$238.36	13.843%	$271.3562	$271.36	$271.35	$271.40
7 purchase totals =	$771.13		$862.6486	$862.64	$862.70	$862.70