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	$124.35	11.849%	$139.0842	$139.08	$139.10	$139.10
Purchase #2	$122.60	8.667%	$133.2257	$133.23	$133.25	$133.20
Purchase #3	$127.89	8.676%	$138.9857	$138.99	$139.00	$139.00
Purchase #4	$98.70	10.785%	$109.3448	$109.34	$109.35	$109.30
Purchase #5	$51.34	8.626%	$55.7686	$55.77	$55.75	$55.80
Purchase #6	$105.47	4.236%	$109.9377	$109.94	$109.95	$109.90
Purchase #7	$67.90	5.736%	$71.7947	$71.79	$71.80	$71.80
7 purchase totals =	$698.25		$758.1414	$758.14	$758.20	$758.10