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	$37.91	12.611%	$42.6908	$42.69	$42.70	$42.70
Purchase #2	$67.94	6.434%	$72.3113	$72.31	$72.30	$72.30
Purchase #3	$68.42	4.138%	$71.2512	$71.25	$71.25	$71.30
Purchase #4	$61.85	9.315%	$67.6113	$67.61	$67.60	$67.60
Purchase #5	$80.89	8.798%	$88.0067	$88.01	$88.00	$88.00
Purchase #6	$89.79	3.589%	$93.0126	$93.01	$93.00	$93.00
Purchase #7	$179.84	5.145%	$189.0928	$189.09	$189.10	$189.10
7 purchase totals =	$586.64		$623.9767	$623.97	$623.95	$624.00