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	$138.93	11.839%	$155.3779	$155.38	$155.40	$155.40
Purchase #2	$225.40	7.593%	$242.5146	$242.51	$242.50	$242.50
Purchase #3	$85.79	4.326%	$89.5013	$89.50	$89.50	$89.50
Purchase #4	$114.27	9.725%	$125.3828	$125.38	$125.40	$125.40
Purchase #5	$62.63	4.155%	$65.2323	$65.23	$65.25	$65.20
Purchase #6	$215.92	9.737%	$236.9441	$236.94	$236.95	$236.90
Purchase #7	$215.56	3.852%	$223.8634	$223.86	$223.85	$223.90
7 purchase totals =	$1,058.50		$1,138.8164	$1,138.80	$1,138.85	$1,138.80