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	$88.94	10.452%	$98.236	$98.24	$98.25	$98.20
Purchase #2	$79.41	4.601%	$83.0637	$83.06	$83.05	$83.10
Purchase #3	$48.72	5.633%	$51.4644	$51.46	$51.45	$51.50
Purchase #4	$42.95	11.646%	$47.952	$47.95	$47.95	$48.00
Purchase #5	$167.71	10.503%	$185.3246	$185.32	$185.30	$185.30
Purchase #6	$98.38	9.755%	$107.977	$107.98	$108.00	$108.00
Purchase #7	$86.86	5.196%	$91.3732	$91.37	$91.35	$91.40
7 purchase totals =	$612.97		$665.3909	$665.38	$665.35	$665.50