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	$36.79	9.555%	$40.3053	$40.31	$40.30	$40.30
Purchase #2	$28.95	9.398%	$31.6707	$31.67	$31.65	$31.70
Purchase #3	$124.59	13.735%	$141.7024	$141.70	$141.70	$141.70
Purchase #4	$91.41	12.811%	$103.1205	$103.12	$103.10	$103.10
Purchase #5	$75.39	7.559%	$81.0887	$81.09	$81.10	$81.10
Purchase #6	$213.39	5.649%	$225.4444	$225.44	$225.45	$225.40
Purchase #7	$103.42	7.747%	$111.4319	$111.43	$111.45	$111.40
7 purchase totals =	$673.94		$734.7639	$734.76	$734.75	$734.70