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	$106.87	13.172%	$120.9469	$120.95	$120.95	$120.90
Purchase #2	$159.46	13.655%	$181.2343	$181.23	$181.25	$181.20
Purchase #3	$155.52	7.311%	$166.8901	$166.89	$166.90	$166.90
Purchase #4	$121.59	8.510%	$131.9373	$131.94	$131.95	$131.90
Purchase #5	$55.55	10.726%	$61.5083	$61.51	$61.50	$61.50
Purchase #6	$47.57	8.638%	$51.6791	$51.68	$51.70	$51.70
Purchase #7	$98.66	6.656%	$105.2268	$105.23	$105.25	$105.20
7 purchase totals =	$745.22		$819.4228	$819.43	$819.50	$819.30