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	$61.67	8.808%	$67.1019	$67.10	$67.10	$67.10
Purchase #2	$125.49	10.702%	$138.9199	$138.92	$138.90	$138.90
Purchase #3	$81.34	3.664%	$84.3203	$84.32	$84.30	$84.30
Purchase #4	$98.38	13.254%	$111.4193	$111.42	$111.40	$111.40
Purchase #5	$38.96	11.531%	$43.4525	$43.45	$43.45	$43.50
Purchase #6	$245.69	11.188%	$273.1778	$273.18	$273.20	$273.20
Purchase #7	$210.29	5.138%	$221.0947	$221.09	$221.10	$221.10
7 purchase totals =	$861.82		$939.4864	$939.48	$939.45	$939.50