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	$25.25	7.377%	$27.1127	$27.11	$27.10	$27.10
Purchase #2	$47.25	12.766%	$53.2819	$53.28	$53.30	$53.30
Purchase #3	$98.45	5.550%	$103.914	$103.91	$103.90	$103.90
Purchase #4	$104.57	9.136%	$114.1235	$114.12	$114.10	$114.10
Purchase #5	$84.61	13.632%	$96.144	$96.14	$96.15	$96.10
Purchase #6	$17.57	13.670%	$19.9718	$19.97	$19.95	$20.00
Purchase #7	$84.52	5.748%	$89.3782	$89.38	$89.40	$89.40
7 purchase totals =	$462.22		$503.9261	$503.91	$503.90	$503.90