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	$150.33	7.478%	$161.5717	$161.57	$161.55	$161.60
Purchase #2	$80.51	12.493%	$90.5681	$90.57	$90.55	$90.60
Purchase #3	$130.54	8.471%	$141.598	$141.60	$141.60	$141.60
Purchase #4	$77.85	7.647%	$83.8032	$83.80	$83.80	$83.80
Purchase #5	$236.95	13.303%	$268.4715	$268.47	$268.45	$268.50
Purchase #6	$54.73	8.395%	$59.3246	$59.32	$59.30	$59.30
Purchase #7	$108.68	3.830%	$112.8424	$112.84	$112.85	$112.80
7 purchase totals =	$839.59		$918.1795	$918.17	$918.10	$918.20