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	$15.49	12.663%	$17.4515	$17.45	$17.45	$17.50
Purchase #2	$186.90	5.113%	$196.4562	$196.46	$196.45	$196.50
Purchase #3	$108.96	9.758%	$119.5923	$119.59	$119.60	$119.60
Purchase #4	$82.51	4.796%	$86.4672	$86.47	$86.45	$86.50
Purchase #5	$165.40	13.745%	$188.1342	$188.13	$188.15	$188.10
Purchase #6	$57.78	13.442%	$65.5468	$65.55	$65.55	$65.50
Purchase #7	$243.90	3.850%	$253.2902	$253.29	$253.30	$253.30
7 purchase totals =	$860.94		$926.9384	$926.94	$926.95	$927.00