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	$104.73	4.370%	$109.3067	$109.31	$109.30	$109.30
Purchase #2	$62.82	10.464%	$69.3935	$69.39	$69.40	$69.40
Purchase #3	$167.45	12.801%	$188.8853	$188.89	$188.90	$188.90
Purchase #4	$46.50	11.218%	$51.7164	$51.72	$51.70	$51.70
Purchase #5	$221.78	9.544%	$242.9467	$242.95	$242.95	$242.90
Purchase #6	$102.56	5.711%	$108.4172	$108.42	$108.40	$108.40
Purchase #7	$67.40	3.307%	$69.6289	$69.63	$69.65	$69.60
7 purchase totals =	$773.24		$840.2947	$840.31	$840.30	$840.20