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	$23.29	11.714%	$26.0182	$26.02	$26.00	$26.00
Purchase #2	$247.66	13.414%	$280.8811	$280.88	$280.90	$280.90
Purchase #3	$193.37	3.458%	$200.0567	$200.06	$200.05	$200.10
Purchase #4	$232.51	13.323%	$263.4873	$263.49	$263.50	$263.50
Purchase #5	$63.52	6.207%	$67.4627	$67.46	$67.45	$67.50
Purchase #6	$212.39	4.460%	$221.8626	$221.86	$221.85	$221.90
Purchase #7	$39.34	3.731%	$40.8078	$40.81	$40.80	$40.80
7 purchase totals =	$1,012.08		$1,100.5764	$1,100.58	$1,100.55	$1,100.70