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	$126.62	12.237%	$142.1145	$142.11	$142.10	$142.10
Purchase #2	$50.93	6.176%	$54.0754	$54.08	$54.10	$54.10
Purchase #3	$97.98	3.821%	$101.7238	$101.72	$101.70	$101.70
Purchase #4	$180.74	8.691%	$196.4481	$196.45	$196.45	$196.40
Purchase #5	$52.66	3.522%	$54.5147	$54.51	$54.50	$54.50
Purchase #6	$66.40	6.782%	$70.9032	$70.90	$70.90	$70.90
Purchase #7	$34.39	9.642%	$37.7059	$37.71	$37.70	$37.70
7 purchase totals =	$609.72		$657.4856	$657.48	$657.45	$657.40