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	$69.71	11.234%	$77.5412	$77.54	$77.55	$77.50
Purchase #2	$78.83	13.506%	$89.4768	$89.48	$89.50	$89.50
Purchase #3	$234.71	12.420%	$263.861	$263.86	$263.85	$263.90
Purchase #4	$163.91	4.103%	$170.6352	$170.64	$170.65	$170.60
Purchase #5	$201.86	13.266%	$228.6387	$228.64	$228.65	$228.60
Purchase #6	$109.85	8.598%	$119.2949	$119.29	$119.30	$119.30
Purchase #7	$24.68	13.506%	$28.0133	$28.01	$28.00	$28.00
7 purchase totals =	$883.55		$977.4611	$977.46	$977.50	$977.40