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	$103.62	13.103%	$117.1973	$117.20	$117.20	$117.20
Purchase #2	$248.54	10.300%	$274.1396	$274.14	$274.15	$274.10
Purchase #3	$49.61	5.571%	$52.3738	$52.37	$52.35	$52.40
Purchase #4	$142.50	7.112%	$152.6346	$152.63	$152.65	$152.60
Purchase #5	$164.27	4.476%	$171.6227	$171.62	$171.60	$171.60
Purchase #6	$104.96	9.398%	$114.8241	$114.82	$114.80	$114.80
Purchase #7	$236.84	5.184%	$249.1178	$249.12	$249.10	$249.10
7 purchase totals =	$1,050.34		$1,131.9099	$1,131.90	$1,131.85	$1,131.80