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	$79.87	11.636%	$89.1637	$89.16	$89.15	$89.20
Purchase #2	$65.34	9.209%	$71.3572	$71.36	$71.35	$71.40
Purchase #3	$187.42	11.738%	$209.4194	$209.42	$209.40	$209.40
Purchase #4	$171.58	3.434%	$177.4721	$177.47	$177.45	$177.50
Purchase #5	$198.94	3.144%	$205.1947	$205.19	$205.20	$205.20
Purchase #6	$106.79	9.481%	$116.9148	$116.91	$116.90	$116.90
Purchase #7	$213.83	13.387%	$242.4554	$242.46	$242.45	$242.50
7 purchase totals =	$1,023.77		$1,111.9773	$1,111.97	$1,111.90	$1,112.10