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	$140.76	10.769%	$155.9184	$155.92	$155.90	$155.90
Purchase #2	$64.67	10.312%	$71.3388	$71.34	$71.35	$71.30
Purchase #3	$65.79	12.130%	$73.7703	$73.77	$73.75	$73.80
Purchase #4	$30.36	3.160%	$31.3194	$31.32	$31.30	$31.30
Purchase #5	$76.58	6.469%	$81.534	$81.53	$81.55	$81.50
Purchase #6	$16.83	7.289%	$18.0567	$18.06	$18.05	$18.10
Purchase #7	$88.60	11.840%	$99.0902	$99.09	$99.10	$99.10
7 purchase totals =	$483.59		$531.0278	$531.03	$531.00	$531.00