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	$164.85	13.587%	$187.2482	$187.25	$187.25	$187.20
Purchase #2	$116.48	10.668%	$128.9061	$128.91	$128.90	$128.90
Purchase #3	$109.81	7.241%	$117.7613	$117.76	$117.75	$117.80
Purchase #4	$30.39	5.498%	$32.0608	$32.06	$32.05	$32.10
Purchase #5	$231.86	11.443%	$258.3917	$258.39	$258.40	$258.40
Purchase #6	$179.67	3.762%	$186.4292	$186.43	$186.45	$186.40
Purchase #7	$249.80	8.287%	$270.5009	$270.50	$270.50	$270.50
7 purchase totals =	$1,082.86		$1,181.2982	$1,181.30	$1,181.30	$1,181.30