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	$21.70	12.740%	$24.4646	$24.46	$24.45	$24.50
Purchase #2	$90.37	13.211%	$102.3088	$102.31	$102.30	$102.30
Purchase #3	$247.85	12.293%	$278.3182	$278.32	$278.30	$278.30
Purchase #4	$60.86	11.536%	$67.8808	$67.88	$67.90	$67.90
Purchase #5	$115.81	13.596%	$131.5555	$131.56	$131.55	$131.60
Purchase #6	$56.97	12.234%	$63.9397	$63.94	$63.95	$63.90
Purchase #7	$183.30	4.731%	$191.9719	$191.97	$191.95	$192.00
7 purchase totals =	$776.86		$860.4395	$860.44	$860.40	$860.50