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	$128.44	8.133%	$138.886	$138.89	$138.90	$138.90
Purchase #2	$120.42	9.166%	$131.4577	$131.46	$131.45	$131.50
Purchase #3	$51.59	8.757%	$56.1077	$56.11	$56.10	$56.10
Purchase #4	$135.49	3.409%	$140.1089	$140.11	$140.10	$140.10
Purchase #5	$196.98	13.410%	$223.395	$223.40	$223.40	$223.40
Purchase #6	$164.78	7.671%	$177.4203	$177.42	$177.40	$177.40
Purchase #7	$247.54	3.576%	$256.392	$256.39	$256.40	$256.40
7 purchase totals =	$1,045.24		$1,123.7676	$1,123.78	$1,123.75	$1,123.80