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	$82.70	9.872%	$90.8641	$90.86	$90.85	$90.90
Purchase #2	$37.33	13.195%	$42.2557	$42.26	$42.25	$42.30
Purchase #3	$57.41	7.498%	$61.7146	$61.71	$61.70	$61.70
Purchase #4	$129.70	13.343%	$147.0059	$147.01	$147.00	$147.00
Purchase #5	$139.41	7.273%	$149.5493	$149.55	$149.55	$149.50
Purchase #6	$35.31	11.787%	$39.472	$39.47	$39.45	$39.50
Purchase #7	$206.45	13.798%	$234.936	$234.94	$234.95	$234.90
7 purchase totals =	$688.31		$765.7976	$765.80	$765.75	$765.80