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	$213.25	7.490%	$229.2224	$229.22	$229.20	$229.20
Purchase #2	$173.86	9.539%	$190.4445	$190.44	$190.45	$190.40
Purchase #3	$37.78	7.447%	$40.5935	$40.59	$40.60	$40.60
Purchase #4	$71.69	12.339%	$80.5358	$80.54	$80.55	$80.50
Purchase #5	$119.70	10.769%	$132.5905	$132.59	$132.60	$132.60
Purchase #6	$146.73	10.555%	$162.2174	$162.22	$162.20	$162.20
Purchase #7	$81.79	11.590%	$91.2695	$91.27	$91.25	$91.30
7 purchase totals =	$844.80		$926.8736	$926.87	$926.85	$926.80