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	$81.73	10.342%	$90.1825	$90.18	$90.20	$90.20
Purchase #2	$27.94	11.801%	$31.2372	$31.24	$31.25	$31.20
Purchase #3	$38.51	13.527%	$43.7192	$43.72	$43.70	$43.70
Purchase #4	$70.46	11.698%	$78.7024	$78.70	$78.70	$78.70
Purchase #5	$243.38	8.321%	$263.6316	$263.63	$263.65	$263.60
Purchase #6	$179.45	4.609%	$187.7209	$187.72	$187.70	$187.70
Purchase #7	$69.45	13.682%	$78.9521	$78.95	$78.95	$79.00
7 purchase totals =	$710.92		$774.1459	$774.14	$774.15	$774.10