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	$97.48	7.125%	$104.4255	$104.43	$104.45	$104.40
Purchase #2	$40.83	13.568%	$46.3698	$46.37	$46.35	$46.40
Purchase #3	$165.93	9.106%	$181.0396	$181.04	$181.05	$181.00
Purchase #4	$110.38	11.582%	$123.1642	$123.16	$123.15	$123.20
Purchase #5	$73.51	10.705%	$81.3792	$81.38	$81.40	$81.40
Purchase #6	$216.93	9.196%	$236.8789	$236.88	$236.90	$236.90
Purchase #7	$42.25	7.250%	$45.3131	$45.31	$45.30	$45.30
7 purchase totals =	$747.31		$818.5703	$818.57	$818.60	$818.60