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	$50.57	13.582%	$57.4384	$57.44	$57.45	$57.40
Purchase #2	$212.60	5.792%	$224.9138	$224.91	$224.90	$224.90
Purchase #3	$226.89	12.426%	$255.0834	$255.08	$255.10	$255.10
Purchase #4	$210.36	7.187%	$225.4786	$225.48	$225.50	$225.50
Purchase #5	$99.85	4.226%	$104.0697	$104.07	$104.05	$104.10
Purchase #6	$47.98	11.744%	$53.6148	$53.61	$53.60	$53.60
Purchase #7	$53.47	11.753%	$59.7543	$59.75	$59.75	$59.80
7 purchase totals =	$901.72		$980.3530	$980.34	$980.35	$980.40