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	$25.65	12.356%	$28.8193	$28.82	$28.80	$28.80
Purchase #2	$196.83	5.399%	$207.4569	$207.46	$207.45	$207.50
Purchase #3	$204.69	6.566%	$218.1299	$218.13	$218.15	$218.10
Purchase #4	$201.31	11.113%	$223.6816	$223.68	$223.70	$223.70
Purchase #5	$196.64	11.740%	$219.7255	$219.73	$219.75	$219.70
Purchase #6	$80.59	11.384%	$89.7644	$89.76	$89.75	$89.80
Purchase #7	$47.58	9.783%	$52.2348	$52.23	$52.25	$52.20
7 purchase totals =	$953.29		$1,039.8124	$1,039.81	$1,039.85	$1,039.80