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	$143.91	11.446%	$160.3819	$160.38	$160.40	$160.40
Purchase #2	$113.84	3.197%	$117.4795	$117.48	$117.50	$117.50
Purchase #3	$192.72	13.357%	$218.4616	$218.46	$218.45	$218.50
Purchase #4	$49.36	9.689%	$54.1425	$54.14	$54.15	$54.10
Purchase #5	$249.50	8.381%	$270.4106	$270.41	$270.40	$270.40
Purchase #6	$112.37	3.333%	$116.1153	$116.12	$116.10	$116.10
Purchase #7	$189.77	9.846%	$208.4548	$208.45	$208.45	$208.50
7 purchase totals =	$1,051.47		$1,145.4462	$1,145.44	$1,145.45	$1,145.50