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	$138.91	11.534%	$154.9319	$154.93	$154.95	$154.90
Purchase #2	$142.25	12.214%	$159.6244	$159.62	$159.60	$159.60
Purchase #3	$94.49	5.122%	$99.3298	$99.33	$99.35	$99.30
Purchase #4	$205.78	9.419%	$225.1624	$225.16	$225.15	$225.20
Purchase #5	$213.82	3.550%	$221.4106	$221.41	$221.40	$221.40
Purchase #6	$145.48	7.336%	$156.1524	$156.15	$156.15	$156.20
Purchase #7	$76.70	5.413%	$80.8518	$80.85	$80.85	$80.90
7 purchase totals =	$1,017.43		$1,097.4633	$1,097.45	$1,097.45	$1,097.50