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	$158.52	12.543%	$178.4032	$178.40	$178.40	$178.40
Purchase #2	$238.46	9.579%	$261.3021	$261.30	$261.30	$261.30
Purchase #3	$169.80	6.869%	$181.4636	$181.46	$181.45	$181.50
Purchase #4	$37.99	11.761%	$42.458	$42.46	$42.45	$42.50
Purchase #5	$97.82	9.472%	$107.0855	$107.09	$107.10	$107.10
Purchase #6	$6.96	4.234%	$7.2547	$7.25	$7.25	$7.30
Purchase #7	$5.90	7.784%	$6.3593	$6.36	$6.35	$6.40
7 purchase totals =	$715.45		$784.3264	$784.32	$784.30	$784.50