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	$28.92	6.474%	$30.7923	$30.79	$30.80	$30.80
Purchase #2	$56.92	4.751%	$59.6243	$59.62	$59.60	$59.60
Purchase #3	$149.63	12.442%	$168.247	$168.25	$168.25	$168.20
Purchase #4	$70.59	6.113%	$74.9052	$74.91	$74.90	$74.90
Purchase #5	$32.48	3.328%	$33.5609	$33.56	$33.55	$33.60
Purchase #6	$108.55	3.295%	$112.1267	$112.13	$112.15	$112.10
Purchase #7	$143.54	3.611%	$148.7232	$148.72	$148.70	$148.70
7 purchase totals =	$590.63		$627.9796	$627.98	$627.95	$627.90