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	$129.61	5.346%	$136.539	$136.54	$136.55	$136.50
Purchase #2	$79.96	11.185%	$88.9035	$88.90	$88.90	$88.90
Purchase #3	$80.76	11.169%	$89.7801	$89.78	$89.80	$89.80
Purchase #4	$158.60	10.787%	$175.7082	$175.71	$175.70	$175.70
Purchase #5	$74.85	7.735%	$80.6396	$80.64	$80.65	$80.60
Purchase #6	$39.60	12.463%	$44.5353	$44.54	$44.55	$44.50
Purchase #7	$134.48	6.645%	$143.4162	$143.42	$143.40	$143.40
7 purchase totals =	$697.86		$759.5219	$759.53	$759.55	$759.40