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	$20.25	10.544%	$22.3852	$22.39	$22.40	$22.40
Purchase #2	$109.56	12.700%	$123.4741	$123.47	$123.45	$123.50
Purchase #3	$57.38	4.773%	$60.1187	$60.12	$60.10	$60.10
Purchase #4	$194.46	4.848%	$203.8874	$203.89	$203.90	$203.90
Purchase #5	$215.73	10.828%	$239.0892	$239.09	$239.10	$239.10
Purchase #6	$131.40	4.557%	$137.3879	$137.39	$137.40	$137.40
Purchase #7	$60.66	8.164%	$65.6123	$65.61	$65.60	$65.60
7 purchase totals =	$789.44		$851.9548	$851.96	$851.95	$852.00