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	$29.88	13.469%	$33.9045	$33.90	$33.90	$33.90
Purchase #2	$226.88	7.788%	$244.5494	$244.55	$244.55	$244.50
Purchase #3	$92.86	10.239%	$102.3679	$102.37	$102.35	$102.40
Purchase #4	$168.75	7.787%	$181.8906	$181.89	$181.90	$181.90
Purchase #5	$167.59	7.253%	$179.7453	$179.75	$179.75	$179.70
Purchase #6	$11.66	5.571%	$12.3096	$12.31	$12.30	$12.30
Purchase #7	$208.76	3.688%	$216.4591	$216.46	$216.45	$216.50
7 purchase totals =	$906.38		$971.2264	$971.23	$971.20	$971.20