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	$72.94	9.506%	$79.8737	$79.87	$79.85	$79.90
Purchase #2	$33.54	10.562%	$37.0825	$37.08	$37.10	$37.10
Purchase #3	$78.33	5.246%	$82.4392	$82.44	$82.45	$82.40
Purchase #4	$29.34	9.214%	$32.0434	$32.04	$32.05	$32.00
Purchase #5	$136.90	3.843%	$142.1611	$142.16	$142.15	$142.20
Purchase #6	$16.72	4.552%	$17.4811	$17.48	$17.50	$17.50
Purchase #7	$75.48	8.366%	$81.7947	$81.79	$81.80	$81.80
7 purchase totals =	$443.25		$472.8757	$472.86	$472.90	$472.90