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	$226.72	13.313%	$256.9032	$256.90	$256.90	$256.90
Purchase #2	$77.57	10.801%	$85.9483	$85.95	$85.95	$85.90
Purchase #3	$142.61	6.319%	$151.6215	$151.62	$151.60	$151.60
Purchase #4	$186.93	4.199%	$194.7792	$194.78	$194.80	$194.80
Purchase #5	$27.82	6.208%	$29.5471	$29.55	$29.55	$29.50
Purchase #6	$225.59	6.258%	$239.7074	$239.71	$239.70	$239.70
Purchase #7	$117.58	11.870%	$131.5367	$131.54	$131.55	$131.50
7 purchase totals =	$1,004.82		$1,090.0434	$1,090.05	$1,090.05	$1,089.90