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	$116.50	6.323%	$123.8663	$123.87	$123.85	$123.90
Purchase #2	$102.77	5.610%	$108.5354	$108.54	$108.55	$108.50
Purchase #3	$100.55	9.197%	$109.7976	$109.80	$109.80	$109.80
Purchase #4	$246.77	9.659%	$270.6055	$270.61	$270.60	$270.60
Purchase #5	$78.26	12.148%	$87.767	$87.77	$87.75	$87.80
Purchase #6	$243.36	8.694%	$264.5177	$264.52	$264.50	$264.50
Purchase #7	$53.31	5.588%	$56.289	$56.29	$56.30	$56.30
7 purchase totals =	$941.52		$1,021.3785	$1,021.40	$1,021.35	$1,021.40