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	$130.72	3.253%	$134.9723	$134.97	$134.95	$135.00
Purchase #2	$247.79	7.554%	$266.5081	$266.51	$266.50	$266.50
Purchase #3	$82.33	10.470%	$90.95	$90.95	$90.95	$91.00
Purchase #4	$209.65	8.377%	$227.2124	$227.21	$227.20	$227.20
Purchase #5	$82.97	10.287%	$91.5051	$91.51	$91.50	$91.50
Purchase #6	$215.84	9.751%	$236.8866	$236.89	$236.90	$236.90
Purchase #7	$32.31	4.618%	$33.8021	$33.80	$33.80	$33.80
7 purchase totals =	$1,001.61		$1,081.8366	$1,081.84	$1,081.80	$1,081.90