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	$250.72	8.698%	$272.5276	$272.53	$272.55	$272.50
Purchase #2	$246.71	9.288%	$269.6244	$269.62	$269.60	$269.60
Purchase #3	$7.91	3.235%	$8.1659	$8.17	$8.15	$8.20
Purchase #4	$95.60	8.108%	$103.3512	$103.35	$103.35	$103.40
Purchase #5	$20.88	3.496%	$21.61	$21.61	$21.60	$21.60
Purchase #6	$150.32	12.132%	$168.5568	$168.56	$168.55	$168.60
Purchase #7	$168.49	4.654%	$176.3315	$176.33	$176.35	$176.30
7 purchase totals =	$940.63		$1,020.1674	$1,020.17	$1,020.15	$1,020.20