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	$24.32	10.647%	$26.9094	$26.91	$26.90	$26.90
Purchase #2	$47.78	3.218%	$49.3176	$49.32	$49.30	$49.30
Purchase #3	$193.47	8.314%	$209.5551	$209.56	$209.55	$209.60
Purchase #4	$130.37	5.800%	$137.9315	$137.93	$137.95	$137.90
Purchase #5	$51.88	5.782%	$54.8797	$54.88	$54.90	$54.90
Purchase #6	$74.57	5.312%	$78.5312	$78.53	$78.55	$78.50
Purchase #7	$205.99	12.331%	$231.3906	$231.39	$231.40	$231.40
7 purchase totals =	$728.38		$788.5151	$788.52	$788.55	$788.50