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	$146.55	10.832%	$162.4243	$162.42	$162.40	$162.40
Purchase #2	$184.79	3.443%	$191.1523	$191.15	$191.15	$191.20
Purchase #3	$128.53	13.860%	$146.3443	$146.34	$146.35	$146.30
Purchase #4	$81.65	10.145%	$89.9334	$89.93	$89.95	$89.90
Purchase #5	$220.36	8.281%	$238.608	$238.61	$238.60	$238.60
Purchase #6	$237.60	13.813%	$270.4197	$270.42	$270.40	$270.40
Purchase #7	$177.83	8.466%	$192.8851	$192.89	$192.90	$192.90
7 purchase totals =	$1,177.31		$1,291.7671	$1,291.76	$1,291.75	$1,291.70