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	$231.94	13.830%	$264.0173	$264.02	$264.00	$264.00
Purchase #2	$159.98	3.601%	$165.7409	$165.74	$165.75	$165.70
Purchase #3	$214.84	4.736%	$225.0148	$225.01	$225.00	$225.00
Purchase #4	$97.68	13.544%	$110.9098	$110.91	$110.90	$110.90
Purchase #5	$198.83	11.831%	$222.3536	$222.35	$222.35	$222.40
Purchase #6	$103.69	10.381%	$114.4541	$114.45	$114.45	$114.50
Purchase #7	$139.55	11.724%	$155.9108	$155.91	$155.90	$155.90
7 purchase totals =	$1,146.51		$1,258.4013	$1,258.39	$1,258.35	$1,258.40