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	$37.72	5.608%	$39.8353	$39.84	$39.85	$39.80
Purchase #2	$138.95	11.539%	$154.9834	$154.98	$155.00	$155.00
Purchase #3	$195.96	11.721%	$218.9285	$218.93	$218.95	$218.90
Purchase #4	$82.34	11.516%	$91.8223	$91.82	$91.80	$91.80
Purchase #5	$24.46	4.555%	$25.5742	$25.57	$25.55	$25.60
Purchase #6	$29.65	9.551%	$32.4819	$32.48	$32.50	$32.50
Purchase #7	$173.52	7.127%	$185.8868	$185.89	$185.90	$185.90
7 purchase totals =	$682.60		$749.5124	$749.51	$749.55	$749.50