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	$243.98	13.443%	$276.7782	$276.78	$276.80	$276.80
Purchase #2	$131.47	12.707%	$148.1759	$148.18	$148.20	$148.20
Purchase #3	$65.65	10.710%	$72.6811	$72.68	$72.70	$72.70
Purchase #4	$135.26	12.668%	$152.3947	$152.39	$152.40	$152.40
Purchase #5	$78.97	13.631%	$89.7344	$89.73	$89.75	$89.70
Purchase #6	$5.59	6.289%	$5.9416	$5.94	$5.95	$5.90
Purchase #7	$65.58	9.305%	$71.6822	$71.68	$71.70	$71.70
7 purchase totals =	$726.50		$817.3881	$817.38	$817.50	$817.40