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	$246.84	13.560%	$280.3115	$280.31	$280.30	$280.30
Purchase #2	$89.46	10.466%	$98.8229	$98.82	$98.80	$98.80
Purchase #3	$171.67	4.799%	$179.9084	$179.91	$179.90	$179.90
Purchase #4	$174.58	4.786%	$182.9354	$182.94	$182.95	$182.90
Purchase #5	$107.73	8.276%	$116.6457	$116.65	$116.65	$116.60
Purchase #6	$153.65	8.398%	$166.5535	$166.55	$166.55	$166.60
Purchase #7	$32.82	5.272%	$34.5503	$34.55	$34.55	$34.60
7 purchase totals =	$976.75		$1,059.7277	$1,059.73	$1,059.70	$1,059.70