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	$46.29	10.203%	$51.013	$51.01	$51.00	$51.00
Purchase #2	$33.57	7.352%	$36.0381	$36.04	$36.05	$36.00
Purchase #3	$203.38	5.728%	$215.0296	$215.03	$215.05	$215.00
Purchase #4	$240.48	8.660%	$261.3056	$261.31	$261.30	$261.30
Purchase #5	$81.60	9.616%	$89.4467	$89.45	$89.45	$89.40
Purchase #6	$162.44	4.228%	$169.308	$169.31	$169.30	$169.30
Purchase #7	$89.48	7.221%	$95.9414	$95.94	$95.95	$95.90
7 purchase totals =	$857.24		$918.0824	$918.09	$918.10	$917.90