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	$150.98	11.764%	$168.7413	$168.74	$168.75	$168.70
Purchase #2	$74.37	8.331%	$80.5658	$80.57	$80.55	$80.60
Purchase #3	$242.42	5.741%	$256.3373	$256.34	$256.35	$256.30
Purchase #4	$12.73	9.513%	$13.941	$13.94	$13.95	$13.90
Purchase #5	$109.85	10.152%	$121.002	$121.00	$121.00	$121.00
Purchase #6	$46.77	10.127%	$51.5064	$51.51	$51.50	$51.50
Purchase #7	$186.60	12.273%	$209.5014	$209.50	$209.50	$209.50
7 purchase totals =	$823.72		$901.5952	$901.60	$901.60	$901.50