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	$126.33	6.302%	$134.2913	$134.29	$134.30	$134.30
Purchase #2	$84.82	5.761%	$89.7065	$89.71	$89.70	$89.70
Purchase #3	$246.96	13.401%	$280.0551	$280.06	$280.05	$280.10
Purchase #4	$163.96	13.466%	$186.0389	$186.04	$186.05	$186.00
Purchase #5	$115.73	3.441%	$119.7123	$119.71	$119.70	$119.70
Purchase #6	$125.37	13.601%	$142.4216	$142.42	$142.40	$142.40
Purchase #7	$142.40	4.341%	$148.5816	$148.58	$148.60	$148.60
7 purchase totals =	$1,005.57		$1,100.8073	$1,100.81	$1,100.80	$1,100.80