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	$45.60	12.711%	$51.3962	$51.40	$51.40	$51.40
Purchase #2	$125.93	5.535%	$132.9002	$132.90	$132.90	$132.90
Purchase #3	$235.90	7.431%	$253.4297	$253.43	$253.45	$253.40
Purchase #4	$82.72	10.394%	$91.3179	$91.32	$91.30	$91.30
Purchase #5	$206.56	9.477%	$226.1357	$226.14	$226.15	$226.10
Purchase #6	$90.75	10.381%	$100.1708	$100.17	$100.15	$100.20
Purchase #7	$162.92	5.542%	$171.949	$171.95	$171.95	$171.90
7 purchase totals =	$950.38		$1,027.2995	$1,027.31	$1,027.30	$1,027.20