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	$203.67	3.270%	$210.33	$210.33	$210.35	$210.30
Purchase #2	$99.41	9.780%	$109.1323	$109.13	$109.15	$109.10
Purchase #3	$250.40	13.130%	$283.2775	$283.28	$283.30	$283.30
Purchase #4	$178.30	12.509%	$200.6035	$200.60	$200.60	$200.60
Purchase #5	$106.61	7.819%	$114.9458	$114.95	$114.95	$114.90
Purchase #6	$116.76	12.185%	$130.9872	$130.99	$131.00	$131.00
Purchase #7	$49.44	4.195%	$51.514	$51.51	$51.50	$51.50
7 purchase totals =	$1,004.59		$1,100.7903	$1,100.79	$1,100.85	$1,100.70