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	$118.97	10.510%	$131.4737	$131.47	$131.45	$131.50
Purchase #2	$124.86	6.785%	$133.3318	$133.33	$133.35	$133.30
Purchase #3	$233.37	12.813%	$263.2717	$263.27	$263.25	$263.30
Purchase #4	$151.80	3.145%	$156.5741	$156.57	$156.55	$156.60
Purchase #5	$247.83	8.703%	$269.3986	$269.40	$269.40	$269.40
Purchase #6	$38.89	13.436%	$44.1153	$44.12	$44.10	$44.10
Purchase #7	$98.48	4.322%	$102.7363	$102.74	$102.75	$102.70
7 purchase totals =	$1,014.20		$1,100.9015	$1,100.90	$1,100.85	$1,100.90