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	$84.76	6.473%	$90.2465	$90.25	$90.25	$90.20
Purchase #2	$93.96	7.761%	$101.2522	$101.25	$101.25	$101.30
Purchase #3	$61.50	6.161%	$65.289	$65.29	$65.30	$65.30
Purchase #4	$166.89	8.801%	$181.578	$181.58	$181.60	$181.60
Purchase #5	$153.49	9.333%	$167.8152	$167.82	$167.80	$167.80
Purchase #6	$109.32	6.705%	$116.6499	$116.65	$116.65	$116.60
Purchase #7	$151.30	12.242%	$169.8221	$169.82	$169.80	$169.80
7 purchase totals =	$821.22		$892.6529	$892.66	$892.65	$892.60