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	$73.36	13.841%	$83.5138	$83.51	$83.50	$83.50
Purchase #2	$159.43	10.460%	$176.1064	$176.11	$176.10	$176.10
Purchase #3	$81.85	5.541%	$86.3853	$86.39	$86.40	$86.40
Purchase #4	$153.30	8.770%	$166.7444	$166.74	$166.75	$166.70
Purchase #5	$64.50	10.806%	$71.4699	$71.47	$71.45	$71.50
Purchase #6	$239.42	7.794%	$258.0804	$258.08	$258.10	$258.10
Purchase #7	$190.59	9.244%	$208.2081	$208.21	$208.20	$208.20
7 purchase totals =	$962.45		$1,050.5083	$1,050.51	$1,050.50	$1,050.50