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	$215.76	3.432%	$223.1649	$223.16	$223.15	$223.20
Purchase #2	$31.78	8.697%	$34.5439	$34.54	$34.55	$34.50
Purchase #3	$51.33	5.309%	$54.0551	$54.06	$54.05	$54.10
Purchase #4	$75.48	12.207%	$84.6938	$84.69	$84.70	$84.70
Purchase #5	$26.73	9.121%	$29.168	$29.17	$29.15	$29.20
Purchase #6	$128.82	4.700%	$134.8745	$134.87	$134.85	$134.90
Purchase #7	$97.65	7.417%	$104.8927	$104.89	$104.90	$104.90
7 purchase totals =	$627.55		$665.3929	$665.38	$665.35	$665.50