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	$92.67	8.498%	$100.5451	$100.55	$100.55	$100.50
Purchase #2	$37.64	11.697%	$42.0428	$42.04	$42.05	$42.00
Purchase #3	$17.33	8.261%	$18.7616	$18.76	$18.75	$18.80
Purchase #4	$28.33	13.352%	$32.1126	$32.11	$32.10	$32.10
Purchase #5	$78.45	11.246%	$87.2725	$87.27	$87.25	$87.30
Purchase #6	$119.90	10.598%	$132.607	$132.61	$132.60	$132.60
Purchase #7	$81.91	5.358%	$86.2987	$86.30	$86.30	$86.30
7 purchase totals =	$456.23		$499.6403	$499.64	$499.60	$499.60