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	$81.94	9.216%	$89.4916	$89.49	$89.50	$89.50
Purchase #2	$28.37	5.831%	$30.0243	$30.02	$30.00	$30.00
Purchase #3	$74.71	9.615%	$81.8934	$81.89	$81.90	$81.90
Purchase #4	$34.91	10.402%	$38.5413	$38.54	$38.55	$38.50
Purchase #5	$41.92	3.814%	$43.5188	$43.52	$43.50	$43.50
Purchase #6	$64.27	11.311%	$71.5396	$71.54	$71.55	$71.50
Purchase #7	$244.38	4.508%	$255.3967	$255.40	$255.40	$255.40
7 purchase totals =	$570.50		$610.4057	$610.40	$610.40	$610.30