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	$104.70	13.254%	$118.5769	$118.58	$118.60	$118.60
Purchase #2	$133.39	13.755%	$151.7378	$151.74	$151.75	$151.70
Purchase #3	$82.67	8.624%	$89.7995	$89.80	$89.80	$89.80
Purchase #4	$168.75	6.613%	$179.9094	$179.91	$179.90	$179.90
Purchase #5	$111.25	11.437%	$123.9737	$123.97	$123.95	$124.00
Purchase #6	$250.29	9.145%	$273.179	$273.18	$273.20	$273.20
Purchase #7	$57.37	5.418%	$60.4783	$60.48	$60.50	$60.50
7 purchase totals =	$908.42		$997.6546	$997.66	$997.70	$997.70