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	$29.87	10.775%	$33.0885	$33.09	$33.10	$33.10
Purchase #2	$24.47	10.805%	$27.114	$27.11	$27.10	$27.10
Purchase #3	$89.87	12.453%	$101.0615	$101.06	$101.05	$101.10
Purchase #4	$188.88	11.153%	$209.9458	$209.95	$209.95	$209.90
Purchase #5	$83.60	5.472%	$88.1746	$88.17	$88.15	$88.20
Purchase #6	$82.71	7.786%	$89.1498	$89.15	$89.15	$89.10
Purchase #7	$98.31	8.346%	$106.515	$106.52	$106.50	$106.50
7 purchase totals =	$597.71		$655.0492	$655.05	$655.00	$655.00