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	$226.30	3.767%	$234.8247	$234.82	$234.80	$234.80
Purchase #2	$114.97	13.584%	$130.5875	$130.59	$130.60	$130.60
Purchase #3	$101.80	7.636%	$109.5734	$109.57	$109.55	$109.60
Purchase #4	$99.31	3.250%	$102.5376	$102.54	$102.55	$102.50
Purchase #5	$20.57	3.332%	$21.2554	$21.26	$21.25	$21.30
Purchase #6	$46.89	4.251%	$48.8833	$48.88	$48.90	$48.90
Purchase #7	$200.57	6.357%	$213.3202	$213.32	$213.30	$213.30
7 purchase totals =	$810.41		$860.9821	$860.98	$860.95	$861.00