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	$56.89	4.834%	$59.6401	$59.64	$59.65	$59.60
Purchase #2	$117.62	13.826%	$133.8821	$133.88	$133.90	$133.90
Purchase #3	$92.84	12.705%	$104.6353	$104.64	$104.65	$104.60
Purchase #4	$82.38	12.355%	$92.558	$92.56	$92.55	$92.60
Purchase #5	$10.98	5.446%	$11.578	$11.58	$11.60	$11.60
Purchase #6	$71.63	11.608%	$79.9448	$79.94	$79.95	$79.90
Purchase #7	$90.48	7.607%	$97.3628	$97.36	$97.35	$97.40
7 purchase totals =	$522.82		$579.6011	$579.60	$579.65	$579.60