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	$143.87	10.585%	$159.0986	$159.10	$159.10	$159.10
Purchase #2	$63.47	6.487%	$67.5873	$67.59	$67.60	$67.60
Purchase #3	$171.75	9.296%	$187.7159	$187.72	$187.70	$187.70
Purchase #4	$27.81	3.871%	$28.8865	$28.89	$28.90	$28.90
Purchase #5	$47.56	12.214%	$53.369	$53.37	$53.35	$53.40
Purchase #6	$187.82	13.378%	$212.9466	$212.95	$212.95	$212.90
Purchase #7	$118.67	6.437%	$126.3088	$126.31	$126.30	$126.30
7 purchase totals =	$760.95		$835.9127	$835.93	$835.90	$835.90