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	$24.90	13.853%	$28.3494	$28.35	$28.35	$28.30
Purchase #2	$49.31	13.383%	$55.9092	$55.91	$55.90	$55.90
Purchase #3	$191.38	5.315%	$201.5518	$201.55	$201.55	$201.60
Purchase #4	$76.25	12.359%	$85.6737	$85.67	$85.65	$85.70
Purchase #5	$114.32	9.241%	$124.8843	$124.88	$124.90	$124.90
Purchase #6	$177.90	7.628%	$191.4702	$191.47	$191.45	$191.50
Purchase #7	$152.36	13.156%	$172.4045	$172.40	$172.40	$172.40
7 purchase totals =	$786.42		$860.2431	$860.23	$860.20	$860.30