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	$92.74	5.680%	$98.0076	$98.01	$98.00	$98.00
Purchase #2	$78.40	8.661%	$85.1902	$85.19	$85.20	$85.20
Purchase #3	$171.79	4.650%	$179.7782	$179.78	$179.80	$179.80
Purchase #4	$59.42	7.172%	$63.6816	$63.68	$63.70	$63.70
Purchase #5	$80.40	9.307%	$87.8828	$87.88	$87.90	$87.90
Purchase #6	$105.30	5.798%	$111.4053	$111.41	$111.40	$111.40
Purchase #7	$183.37	9.225%	$200.2859	$200.29	$200.30	$200.30
7 purchase totals =	$771.42		$826.2316	$826.24	$826.30	$826.30