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	$221.43	12.562%	$249.246	$249.25	$249.25	$249.20
Purchase #2	$105.64	10.160%	$116.373	$116.37	$116.35	$116.40
Purchase #3	$36.83	3.779%	$38.2218	$38.22	$38.20	$38.20
Purchase #4	$97.87	12.281%	$109.8894	$109.89	$109.90	$109.90
Purchase #5	$186.51	4.830%	$195.5184	$195.52	$195.50	$195.50
Purchase #6	$105.88	10.360%	$116.8492	$116.85	$116.85	$116.80
Purchase #7	$136.69	6.412%	$145.4546	$145.45	$145.45	$145.50
7 purchase totals =	$890.85		$971.5524	$971.55	$971.50	$971.50