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	$72.61	13.664%	$82.5314	$82.53	$82.55	$82.50
Purchase #2	$237.98	9.689%	$261.0379	$261.04	$261.05	$261.00
Purchase #3	$45.75	9.423%	$50.061	$50.06	$50.05	$50.10
Purchase #4	$85.47	4.244%	$89.0973	$89.10	$89.10	$89.10
Purchase #5	$244.92	11.845%	$273.9308	$273.93	$273.95	$273.90
Purchase #6	$78.49	9.200%	$85.7111	$85.71	$85.70	$85.70
Purchase #7	$14.62	9.832%	$16.0574	$16.06	$16.05	$16.10
7 purchase totals =	$779.84		$858.4269	$858.43	$858.45	$858.40