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	$66.50	10.380%	$73.4027	$73.40	$73.40	$73.40
Purchase #2	$11.60	7.510%	$12.4712	$12.47	$12.45	$12.50
Purchase #3	$35.39	8.818%	$38.5107	$38.51	$38.50	$38.50
Purchase #4	$249.74	12.700%	$281.457	$281.46	$281.45	$281.50
Purchase #5	$103.72	5.273%	$109.1892	$109.19	$109.20	$109.20
Purchase #6	$140.96	6.725%	$150.4396	$150.44	$150.45	$150.40
Purchase #7	$19.99	7.135%	$21.4163	$21.42	$21.40	$21.40
7 purchase totals =	$627.90		$686.8867	$686.89	$686.85	$686.90