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	$123.98	8.762%	$134.8431	$134.84	$134.85	$134.80
Purchase #2	$168.93	12.416%	$189.9043	$189.90	$189.90	$189.90
Purchase #3	$30.51	9.700%	$33.4695	$33.47	$33.45	$33.50
Purchase #4	$55.97	11.257%	$62.2705	$62.27	$62.25	$62.30
Purchase #5	$188.45	11.273%	$209.694	$209.69	$209.70	$209.70
Purchase #6	$38.90	8.619%	$42.2528	$42.25	$42.25	$42.30
Purchase #7	$248.55	12.646%	$279.9816	$279.98	$280.00	$280.00
7 purchase totals =	$855.29		$952.4158	$952.40	$952.40	$952.50