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	$24.96	11.397%	$27.8047	$27.80	$27.80	$27.80
Purchase #2	$103.62	11.833%	$115.8814	$115.88	$115.90	$115.90
Purchase #3	$59.32	13.312%	$67.2167	$67.22	$67.20	$67.20
Purchase #4	$161.38	4.415%	$168.5049	$168.50	$168.50	$168.50
Purchase #5	$91.75	6.653%	$97.8541	$97.85	$97.85	$97.90
Purchase #6	$243.55	4.227%	$253.8449	$253.84	$253.85	$253.80
Purchase #7	$35.88	5.671%	$37.9148	$37.91	$37.90	$37.90
7 purchase totals =	$720.46		$769.0215	$769.00	$769.00	$769.00