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	$105.33	3.258%	$108.7617	$108.76	$108.75	$108.80
Purchase #2	$54.81	3.870%	$56.9311	$56.93	$56.95	$56.90
Purchase #3	$81.28	10.661%	$89.9453	$89.95	$89.95	$89.90
Purchase #4	$136.41	3.652%	$141.3917	$141.39	$141.40	$141.40
Purchase #5	$61.99	10.433%	$68.4574	$68.46	$68.45	$68.50
Purchase #6	$125.96	12.804%	$142.0879	$142.09	$142.10	$142.10
Purchase #7	$214.79	3.767%	$222.8811	$222.88	$222.90	$222.90
7 purchase totals =	$780.57		$830.4562	$830.46	$830.50	$830.50